fix(#589): show in-session model picker when user sends /model (#596)

* fix(#589): show in-session model picker when user sends /model

Typing a bare '/model' in the chat composer now opens the model picker so
the user can hot-swap the CURRENT session's model via the existing
slash-command path, instead of hand-typing the provider/model string.

- ChatViewModel.preloadModelOptions() caches GET /api/model/options at
  GatewayReady so the picker opens instantly; falls back to on-demand
  refresh if opened before preload finishes.
- sendMessage() intercepts a bare '/model' (no arg) -> showModelPicker=true
  instead of dispatching; a typed '/model provider/model' still dispatches
  via handleSlashCommand.
- sendSlashModel() routes through command.dispatch with session_id, so the
  swap is session-scoped (not the global POST /api/model/set).
- Extracted ModelPickerDialog into ui/model/components and reused by both
  ModelScreen and ChatScreen (adds loading + empty states).
- Added a top-bar model chip (current session model label) that opens the
  same picker.
- Added unit tests: bare /model opens picker, picker selection hot-swaps via
  slash dispatch with session_id, typed /model with arg dispatches directly.

Note: CI shows 2 pre-existing test failures (ChatViewModelTest.testToggleSearch,
HermesWsClientTest.testAutoReconnect) that also fail on a clean main full
suite (MockK static-mock leakage between classes). Unrelated to this change;
compile + ktlint + the 3 new tests pass.

* fix(#589): use backend-valid session-scoped /model command syntax

The model picker now dispatches the canonical backend command form
'/model <model> --provider <slug> --session' instead of the unsupported
'provider/model' slash form. The '--session' flag keeps the switch scoped
to the current chat only (per-session override) and never writes the global
model config, which matches the backend model-switch contract.

- sendSlashModel builds '/model $model --provider $provider --session'.
- Updated unit tests to assert the corrected arg payload
  ('gpt-4o --provider openai --session') and the fully-typed dispatch path.

* fix(#589): add pinned-models section to in-session model picker

- ModelPickerDialog now renders a Pinned section (mirrors global model screen)
- search filter matches model names too, not just provider name/slug
- ChatUiState gains modelPickerPinned, fed from AuthManager.getPinnedModels()
- top-bar model chip removed; picker opens on /model only
- test mock for getPinnedModels() added

* fix(#589): route /model via prompt.submit instead of command.dispatch (resolves 4018)

/model is a real backend slash command handled in the backend's message
pipeline (_handle_message -> _handle_model_command), so it must arrive as
a normal prompt.submit message, not the command.dispatch RPC (which only
knows quick/plugin/bundle/skill commands and 4018s on /model).

- SlashCommandDispatcher: add SlashResult.ModelSwitch, map /model -> ModelSwitch
- ChatViewModel: handle ModelSwitch -> handleModelSwitch() sends via
  WsMethods.PROMPT_SUBMIT with {session_id, text}
- Tests: rewrite the two /model tests to assert prompt.submit (previously
  asserted the buggy command.dispatch path); add /model -> ModelSwitch test

Independent agy review: APPROVE, no blocking issues.

* fix(#589): route /model via slash.exec (correct transport; prompt.submit made LLM treat it as text)

Earlier attempt routed /model through prompt.submit, but the TUI gateway's
prompt.submit handler does NOT parse slash commands — it runs the text as a
normal agent turn, so the LLM received '/model ...' as a user message (the
exact reported bug). The correct RPC is slash.exec, which runs the command
through the slash worker and _mirror_slash_side_effects -> _apply_model_switch
to hot-swap the live session model. command.dispatch is also wrong (only knows
quick/plugin/bundle/skill commands -> 4018).

- WsMethods: add SLASH_EXEC = "slash.exec"
- ChatViewModel.handleModelSwitch: send slash.exec with {command, session_id}
  (previously prompt.submit with {text}); corrected doc comment
- SlashCommandDispatcher: corrected comments (slash.exec, not prompt.submit)
- ChatViewModelTest: rewrite both /model tests to assert slash.exec with the
  /model <model> --provider <slug> --session command string
- SlashCommandDispatcherTest: /model -> ModelSwitch already covered

Verified against hermes-agent tui_gateway/server.py: slash.exec (L13190) ->
worker.run + _mirror_slash_side_effects (L13299) -> _apply_model_switch (L13118);
parse_model_flags accepts --provider/--session (hermes_cli/model_switch.py:355).

Independent agy review of the prior attempt: APPROVE (the wrong-transport
assumption was the author's, not agy's).

* fix(#589): route /model via config.set key=model (slash.exec 4001'd; prompt.submit made LLM treat it as text)

Third transport attempt, now verified against the gateway source:
- prompt.submit: gateway runs text as a normal agent turn -> LLM sees '/model'
  as a message (the original reported bug). WRONG.
- slash.exec: gateway returns 4001 'session not found'. The slash worker path
  resolves the session differently / requires agent-built state the mobile
  session isn't in at switch time. WRONG.
- config.set key=model: gateway (server.py config.set L10253) routes key=='model'
  straight to _apply_model_switch using the SAME _sessions.get(session_id)
  lookup that the working command.dispatch uses. CORRECT.

sendSlashModel still builds '/model <model> --provider <slug> --session';
parse_model_flags (hermes_cli/model_switch.py:355) extracts model/provider/
session from it. handleModelSwitch now sends config.set {key:model, value:
command, session_id}.

- WsMethods: add CONFIG_SET = 'config.set'
- ChatViewModel.handleModelSwitch: config.set instead of slash.exec
- SlashCommandDispatcher: comments updated (config.set, not slash.exec)
- ChatViewModelTest: both /model tests assert config.set key=model + command
- also fixes the MockK testToggleSearch flake by preloading byte-buddy agent
  via JAVA_TOOL_OPTIONS locally (container blocks JVM self-attach)

* fix(#589): strip /model prefix before config.set key=model (5001 'model names can't have spaces')

config.set key=model passes the value DIRECTLY to parse_model_flags — it does
NOT strip a leading '/model' the way slash.exec / prompt.submit do. Sending
'/model <model> ...' made parse_model_flags treat '/model <model>' as the
model name (contains a space) -> 5001.

handleModelSwitch now strips the '/model' prefix and sends the bare spec
'<model> --provider <slug> --session', matching the TUI client's
modelValueForConfigSet (ui-tui session.ts:23) used by useMainApp.ts:123.

- ChatViewModel.handleModelSwitch: spec = command.removePrefix('/model').trim()
- ChatViewModelTest: assert bare spec 'gpt-4o --provider openai --session'
- comment updated

* fix(#589): strip /model prefix case-insensitively before config.set

SlashCommandDispatcher and isModelPickerCommand match /model
case-insensitively, but handleModelSwitch used removePrefix("/model")
(case-sensitive). A typed /MODEL ... forwarded the literal slash prefix
to config.set and the backend's parse_model_flags wouldn't recognize it
— silent hot-swap failure.

Use startsWith("/model", ignoreCase=true) + substring(6) so any casing
is stripped. Added a regression test asserting /MODEL does not forward a
leading slash.

* fix(test): inject searchDispatcher to fix MockKException in testToggleSearch

---------

Co-authored-by: M57 <m57@hermes-control.app>

app/src/main/java/com/m57/hermescontrol/data/ws/WsMethods.kt

@@ -25,6 +25,8 @@ object WsMethods {
     const val COMMANDS_CATALOG = "commands.catalog"
     const val COMMAND_DISPATCH = "command.dispatch"
     const val COMMAND_RESOLVE = "command.resolve"
+    const val SLASH_EXEC = "slash.exec"
+    const val CONFIG_SET = "config.set"
 
     // ── Attachments ───────────────────────────────────────────────────────