Add weather feature with WeatherKit integration for mood entries

Fetch and display weather data (temp, condition, hi/lo, humidity) when
users log a mood. Weather is stored as JSON on MoodEntryModel and shown
as a card in EntryDetailView. Premium-gated with location permission
prompt. Includes BGTask retry for failed fetches and full analytics.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Shared/Models/WeatherData.swift

@@ -0,0 +1,32 @@
+//
+//  WeatherData.swift
+//  Reflect
+//
+//  Codable weather model stored as JSON string in MoodEntryModel.
+//
+
+import Foundation
+
+struct WeatherData: Codable {
+    let conditionSymbol: String    // SF Symbol from WeatherKit (e.g. "cloud.sun.fill")
+    let condition: String          // "Partly Cloudy"
+    let temperature: Double        // Current/average in Celsius
+    let highTemperature: Double    // Day high in Celsius
+    let lowTemperature: Double     // Day low in Celsius
+    let humidity: Double           // 0.0–1.0
+    let latitude: Double
+    let longitude: Double
+    let fetchedAt: Date
+
+    // MARK: - JSON Helpers
+
+    func encode() -> String? {
+        guard let data = try? JSONEncoder().encode(self) else { return nil }
+        return String(data: data, encoding: .utf8)
+    }
+
+    static func decode(from json: String) -> WeatherData? {
+        guard let data = json.data(using: .utf8) else { return nil }
+        return try? JSONDecoder().decode(WeatherData.self, from: data)
+    }
+}