Add AI-powered insights using Apple Foundation Models

- Replace static insights with on-device AI generation via FoundationModels framework
- Add @Generable AIInsight model for structured LLM output
- Create FoundationModelsInsightService with session-per-request for concurrent generation
- Add MoodDataSummarizer to prepare mood data for AI analysis
- Implement loading states with skeleton UI and pull-to-refresh
- Add AI availability badge and error handling
- Support default (supportive) and rude (sarcastic) personality modes
- Optimize prompts to fit within 4096 token context limit
- Bump iOS deployment target to 26.0 for Foundation Models support

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Shared/Models/AIInsight.swift

@@ -0,0 +1,68 @@
+//
+//  AIInsight.swift
+//  Feels
+//
+//  Created by Claude Code on 12/13/24.
+//
+
+import Foundation
+import FoundationModels
+
+/// Represents a single AI-generated insight using @Generable for structured LLM output
+@Generable
+struct AIInsight: Equatable {
+    @Guide(description: "A brief, engaging title for the insight (3-6 words)")
+    var title: String
+
+    @Guide(description: "A detailed, personalized description of the insight (1-2 sentences)")
+    var description: String
+
+    @Guide(description: "The type of insight: pattern (observed trend), advice (recommendation), prediction (future forecast), achievement (milestone), or trend (direction analysis)")
+    var insightType: String
+
+    @Guide(description: "The primary mood associated with this insight: great, good, average, bad, horrible, or none")
+    var associatedMood: String
+
+    @Guide(description: "SF Symbol name for the insight icon (e.g., star.fill, chart.line.uptrend.xyaxis, heart.fill)")
+    var iconName: String
+
+    @Guide(description: "Sentiment of the insight: positive, neutral, or negative")
+    var sentiment: String
+}
+
+/// Container for period-specific insights - the LLM generates this structure
+@Generable
+struct AIInsightsResponse: Equatable {
+    @Guide(description: "Array of exactly 5 diverse insights covering patterns, advice, and predictions")
+    var insights: [AIInsight]
+}
+
+// MARK: - Conversion to App's Insight Model
+
+extension AIInsight {
+    /// Converts AI-generated insight to the app's existing Insight model
+    func toInsight() -> Insight {
+        let mood: Mood? = switch associatedMood.lowercased() {
+        case "great": .great
+        case "good": .good
+        case "average": .average
+        case "bad": .bad
+        case "horrible": .horrible
+        default: nil
+        }
+
+        return Insight(
+            icon: iconName,
+            title: title,
+            description: description,
+            mood: mood
+        )
+    }
+}
+
+extension AIInsightsResponse {
+    /// Converts all AI insights to app's Insight models
+    func toInsights() -> [Insight] {
+        insights.map { $0.toInsight() }
+    }
+}