fix(#686): implement robust history pagination (#687)

* fix(#686): implement robust history pagination

Honor server-returned offset, degrade gracefully on older servers, and parse JSON tool results.

* fix(ci): repair unit-test compilation and pagination test mocks

- Remove trailing blank line in SessionMessagesResponse.kt (ktlint)
- Replace unresolved io.mockk.eq/coAnswers usage in ChatViewModelTest with
  an ordered-call counter inside coAnswers, which compiles and runs on
  MockK 1.14.11 (eq is a matcher-scope member, not a top-level import)
- Align HermesApiServiceMockWebServerTest with the PR's JsonElement content
  model (contentText) and the new include_compacted=true default query param

All unit tests pass locally with the ByteBuddy agent preload.

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/data/model/SessionMessagesResponse.kt

@@ -1,4 +1,5 @@
 package com.m57.hermescontrol.data.model
+
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonPrimitive
@@ -6,15 +7,25 @@ import kotlinx.serialization.json.JsonPrimitive
 @Serializable
 data class SessionMessagesResponse(
     val messages: List<SessionMessage>,
+    val offset: Int? = null,
+    val total: Int? = null,
 )
 
 @Serializable
 data class SessionMessage(
     val role: String? = null,
-    val content: String? = null,
+    val content: JsonElement? = null,
     val timestamp: JsonElement? = null,
     val type: String? = null,
 ) {
     val timestampText: String?
         get() = (timestamp as? JsonPrimitive)?.content
+
+    val contentText: String
+        get() =
+            when (content) {
+                is JsonPrimitive -> content.content
+                null -> ""
+                else -> content.toString()
+            }
 }