v1.14: usage history chart + threshold notifications

Add an in-app 7-day history chart and opt-in usage alerts, the two
features requested from the macOS Claude-Usage-Tracker that map cleanly
to an Android widget app.

History:
- UsageSnapshot model; PreferencesManager records session/weekly
  utilization on every refresh (7-day retention, <=600 points, collapses
  readings under 2 min apart to avoid worker+manual double-logging).
- HistoryChartView: dependency-free Canvas line chart (session/weekly,
  0/50/100% gridlines), breaks the line across >35-min gaps.
- New HISTORY card with chart + legend.

Notifications:
- Notifier posts when session/weekly crosses a user threshold, at most
  once per limit window (keyed on reset-epoch, re-arms on rollover).
- USAGE ALERTS card: enable switch + session/weekly sliders (50-100%,
  defaults 90/85). POST_NOTIFICATIONS permission + runtime request.
- Wired into the existing 5-min background worker.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/java/me/khodak/claudeusage/data/PreferencesManager.kt

@@ -4,6 +4,7 @@ import android.content.Context
 import androidx.security.crypto.EncryptedSharedPreferences
 import androidx.security.crypto.MasterKey
 import com.google.gson.Gson
+import com.google.gson.reflect.TypeToken
 import java.util.Calendar
 
 class PreferencesManager(context: Context) {
@@ -73,6 +74,61 @@ class PreferencesManager(context: Context) {
 
     fun isLoggedIn(): Boolean = !getCookies().isNullOrBlank()
 
+    // ── Usage history (for the in-app chart) ─────────────────────────────────
+
+    /**
+     * Append a history point if [data] carries a real utilization reading.
+     * De-duplicates rapid double-fires (manual refresh + background worker landing
+     * together) by skipping points within [MIN_HISTORY_GAP_MS] of the last one, and
+     * prunes anything older than [HISTORY_RETENTION_MS] / beyond [MAX_HISTORY_POINTS].
+     */
+    fun recordHistory(data: UsageData) {
+        if (data.fiveHourUtilization < 0f && data.weeklyUtilization < 0f) return
+        val now = System.currentTimeMillis()
+        val history = getHistory().toMutableList()
+        if (history.isNotEmpty() && now - history.last().epochMs < MIN_HISTORY_GAP_MS) {
+            history.removeAt(history.size - 1) // collapse near-simultaneous readings
+        }
+        history.add(
+            UsageSnapshot(
+                epochMs = now,
+                sessionPct = data.fiveHourUtilization,
+                weeklyPct = data.weeklyUtilization
+            )
+        )
+        val cutoff = now - HISTORY_RETENTION_MS
+        val pruned = history.filter { it.epochMs >= cutoff }
+            .takeLast(MAX_HISTORY_POINTS)
+        prefs.edit().putString(KEY_HISTORY, gson.toJson(pruned)).apply()
+    }
+
+    fun getHistory(): List<UsageSnapshot> {
+        val json = prefs.getString(KEY_HISTORY, null) ?: return emptyList()
+        return try {
+            val type = object : TypeToken<List<UsageSnapshot>>() {}.type
+            gson.fromJson<List<UsageSnapshot>>(json, type) ?: emptyList()
+        } catch (e: Exception) { emptyList() }
+    }
+
+    // ── Notification settings ────────────────────────────────────────────────
+
+    fun isNotifyEnabled(): Boolean = prefs.getBoolean(KEY_NOTIFY_ENABLED, true)
+    fun setNotifyEnabled(v: Boolean) = prefs.edit().putBoolean(KEY_NOTIFY_ENABLED, v).apply()
+
+    fun getSessionThreshold(): Int = prefs.getInt(KEY_NOTIFY_SESSION_PCT, 90)
+    fun setSessionThreshold(pct: Int) = prefs.edit().putInt(KEY_NOTIFY_SESSION_PCT, pct).apply()
+
+    fun getWeeklyThreshold(): Int = prefs.getInt(KEY_NOTIFY_WEEKLY_PCT, 85)
+    fun setWeeklyThreshold(pct: Int) = prefs.edit().putInt(KEY_NOTIFY_WEEKLY_PCT, pct).apply()
+
+    /**
+     * Tracks the reset-epoch a metric was last notified for, so we alert at most once
+     * per limit window. When the window rolls over (reset epoch changes), it re-arms.
+     */
+    fun getNotifiedResetEpoch(key: String): Long = prefs.getLong("notified_$key", 0L)
+    fun setNotifiedResetEpoch(key: String, epoch: Long) =
+        prefs.edit().putLong("notified_$key", epoch).apply()
+
     companion object {
         private const val KEY_COOKIES = "session_cookies"
         private const val KEY_ORG_ID = "org_id"
@@ -80,6 +136,14 @@ class PreferencesManager(context: Context) {
         private const val KEY_USAGE_DATA = "usage_data"
         private const val KEY_ACTIVE_WEEK = "active_week"
         private const val KEY_ACTIVE_MASK = "active_mask"
+        private const val KEY_HISTORY = "usage_history"
+        private const val KEY_NOTIFY_ENABLED = "notify_enabled"
+        private const val KEY_NOTIFY_SESSION_PCT = "notify_session_pct"
+        private const val KEY_NOTIFY_WEEKLY_PCT = "notify_weekly_pct"
+
+        private const val MIN_HISTORY_GAP_MS = 2 * 60 * 1000L      // collapse readings <2 min apart
+        private const val HISTORY_RETENTION_MS = 7 * 24 * 60 * 60 * 1000L  // keep 7 days
+        private const val MAX_HISTORY_POINTS = 600
 
         fun createSecurePrefs(context: Context, onFallback: (() -> Unit)? = null): android.content.SharedPreferences {
             return try {