refactor(cleanup): remove 5 orphaned symbols (no behavior change) (#484)

- ChatViewModel: drop fetchAndDisplayStatus/Sessions/Stats — left behind
  after slash-command dispatch rework (e7b2973c); /status /sessions /stats
  now route to backend via SlashCommandDispatcher.RpcDispatch -> WS COMMAND_DISPATCH.
  Zero call sites, grep-confirmed.
- AuthManager: drop KEY_SELECTED_PROFILE_ID const — selected profile id
  moved to ServerStore StateFlow (getSelectedProfileId/setSelectedProfileId).
  Legacy PREFS key never read.
- Theme: drop ENABLE_DYNAMIC_COLOR const — theming reads useDynamicColors
  setting (Theme.kt:318), not this const. Dead since that refactor.

Verification: ktlintCheck PASS, compileDebugKotlin PASS (local SDK).
Per behavior-preserving-cleanup: grep zero refs, not exported, no
dynamic/reflection access, git blame shows original intent superseded.

app/src/main/java/com/m57/hermescontrol/theme/Theme.kt

@@ -26,11 +26,6 @@ enum class BottomNavDisplayMode { ICON_AND_TEXT, ICON_ONLY, TEXT_ONLY }
 val LocalThemePreference = compositionLocalOf { ThemePreference.SYSTEM }
 val LocalThemePreset = compositionLocalOf { ThemePreset.DEFAULT }
 
-/**
- * Set to true to opt into Material You dynamic color (Android 12+).
- */
-private const val ENABLE_DYNAMIC_COLOR = true
-
 private val HermesDarkColorScheme =
     darkColorScheme(
         primary = HermesPurple,