feat(#537): analytics screen — usage + per-model stats (#558)

* feat(#537): analytics screen — usage + per-model stats from /api/analytics/*

* fix(#537): address PR review — cancel-in-flight loads, retain cache on refresh, drop redundant async

* fix(#537): surface real analytics failure, mirror backend shape (period_days/tools), round-trip test

* fix(#537): tolerate float last_used_at in analytics (backend emits epoch as number)

* fix(#537): type tools[] as AnalyticsToolUsage (tool/count/percentage), render Top tools section

* fix(analytics): fix crashes and refactor tab layout

* perf(analytics): cache responses and prefetch day windows

---------

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

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

@@ -0,0 +1,125 @@
+package com.m57.hermescontrol.data.model
+
+import kotlinx.serialization.Serializable
+
+/**
+ * Usage analytics over a trailing window, returned by `GET /api/analytics/usage`.
+ * Mirrors `web/src/lib/api.ts` `AnalyticsResponse`.
+ */
+@Serializable
+data class AnalyticsResponse(
+    val daily: List<AnalyticsDailyEntry> = emptyList(),
+    val by_model: List<AnalyticsModelEntry> = emptyList(),
+    val totals: AnalyticsTotals = AnalyticsTotals(),
+    val period_days: Int = 0,
+    val skills: AnalyticsSkills = AnalyticsSkills(),
+    val tools: List<AnalyticsToolUsage> = emptyList(),
+)
+
+@Serializable
+data class AnalyticsToolUsage(
+    val tool: String = "",
+    val count: Int = 0,
+    val percentage: Double = 0.0,
+)
+
+@Serializable
+data class AnalyticsDailyEntry(
+    val day: String = "",
+    val input_tokens: Long = 0,
+    val output_tokens: Long = 0,
+    val cache_read_tokens: Long = 0,
+    val reasoning_tokens: Long = 0,
+    val estimated_cost: Double = 0.0,
+    val actual_cost: Double = 0.0,
+    val sessions: Int = 0,
+    val api_calls: Int = 0,
+)
+
+@Serializable
+data class AnalyticsModelEntry(
+    val model: String = "",
+    val input_tokens: Long = 0,
+    val output_tokens: Long = 0,
+    val estimated_cost: Double = 0.0,
+    val sessions: Int = 0,
+    val api_calls: Int = 0,
+)
+
+@Serializable
+data class AnalyticsTotals(
+    val total_input: Long = 0,
+    val total_output: Long = 0,
+    val total_cache_read: Long = 0,
+    val total_reasoning: Long = 0,
+    val total_estimated_cost: Double = 0.0,
+    val total_actual_cost: Double = 0.0,
+    val total_sessions: Int = 0,
+    val total_api_calls: Int = 0,
+)
+
+@Serializable
+data class AnalyticsSkills(
+    val summary: AnalyticsSkillsSummary = AnalyticsSkillsSummary(),
+    val top_skills: List<AnalyticsSkillEntry> = emptyList(),
+)
+
+@Serializable
+data class AnalyticsSkillEntry(
+    val skill: String = "",
+    val view_count: Int = 0,
+    val manage_count: Int = 0,
+    val total_count: Int = 0,
+    val percentage: Double = 0.0,
+    val last_used_at: Double? = null,
+)
+
+@Serializable
+data class AnalyticsSkillsSummary(
+    val total_skill_loads: Int = 0,
+    val total_skill_edits: Int = 0,
+    val total_skill_actions: Int = 0,
+    val distinct_skills_used: Int = 0,
+)
+
+/**
+ * Per-model analytics over a trailing window, returned by
+ * `GET /api/analytics/models`. Mirrors `web/src/lib/api.ts`
+ * `ModelsAnalyticsResponse`.
+ */
+@Serializable
+data class ModelsAnalyticsResponse(
+    val models: List<ModelsAnalyticsModelEntry> = emptyList(),
+    val totals: ModelsAnalyticsTotals = ModelsAnalyticsTotals(),
+    val period_days: Int = 0,
+)
+
+@Serializable
+data class ModelsAnalyticsModelEntry(
+    val model: String = "",
+    val provider: String = "",
+    val input_tokens: Long = 0,
+    val output_tokens: Long = 0,
+    val cache_read_tokens: Long = 0,
+    val reasoning_tokens: Long = 0,
+    val estimated_cost: Double = 0.0,
+    val actual_cost: Double = 0.0,
+    val sessions: Int = 0,
+    val api_calls: Int = 0,
+    val tool_calls: Int = 0,
+    val last_used_at: Double? = null,
+    val avg_tokens_per_session: Double = 0.0,
+)
+
+@Serializable
+data class ModelsAnalyticsTotals(
+    val distinct_models: Int = 0,
+    val total_input: Long = 0,
+    val total_output: Long = 0,
+    val total_cache_read: Long = 0,
+    val total_reasoning: Long = 0,
+    val total_estimated_cost: Double = 0.0,
+    val total_actual_cost: Double = 0.0,
+    val total_sessions: Int = 0,
+    val total_api_calls: Int = 0,
+)