Phase 3: usage screen

GET /usage serves the numbers behind Claude Code's /usage, read with the
CLI's own stored OAuth credentials (nothing to configure). The endpoint
is undocumented, so parsing is defensive -- the generic limits[] array
becomes labeled window bars, unknown kinds surface under their raw name,
and any failure degrades to an 'unavailable' snapshot with the reason.
One UsageProvider per paid service behind a caching monitor that
enforces the >=180s minimum poll regardless of phone refreshes; no
background polling at all. ureq (rustls) does the outbound call, with
the process-level CryptoProvider now chosen explicitly in main -- ureq
brings ring while axum-server brings aws-lc-rs, and with both in the
graph rustls refuses to guess.

App: a Usage screen off the session list -- per-window bars colored by
utilization with relative reset times. Verified live: 74%/26%/16%
windows rendered against the real endpoint.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

app/androidApp/src/main/kotlin/com/example/aiapp/Api.kt

@@ -195,6 +195,45 @@ fun fetchSessionFile(settings: ServerSettings, sessionId: String, name: String):
         it.inputStream.readBytes()
     }
 
+// One rate-limit window, rendered as a labeled bar on the usage screen.
+data class UsageWindow(
+    val label: String,
+    val percent: Double,
+    val resetsAt: String?,
+    val active: Boolean,
+)
+
+data class UsageSnapshot(
+    val provider: String,
+    val available: Boolean,
+    val windows: List<UsageWindow>,
+    val error: String?,
+)
+
+/** The backend caches; refreshing more often than its poll interval just re-reads the cache. */
+fun fetchUsage(settings: ServerSettings): List<UsageSnapshot> =
+    requestFromServer(settings, "/usage", readTimeoutMs = 30000) { connection ->
+        val snapshots = JSONArray(connection.inputStream.bufferedReader().readText())
+        (0 until snapshots.length()).map { i ->
+            val snapshot = snapshots.getJSONObject(i)
+            val windows = snapshot.getJSONArray("windows")
+            UsageSnapshot(
+                provider = snapshot.getString("provider"),
+                available = snapshot.getBoolean("available"),
+                error = snapshot.optString("error").ifEmpty { null },
+                windows = (0 until windows.length()).map { j ->
+                    val window = windows.getJSONObject(j)
+                    UsageWindow(
+                        label = window.getString("label"),
+                        percent = window.getDouble("percent"),
+                        resetsAt = window.optString("resetsAt").ifEmpty { null },
+                        active = window.getBoolean("active"),
+                    )
+                },
+            )
+        }
+    }
+
 fun answerQuestion(settings: ServerSettings, sessionId: String, questionId: String, answer: String) {
     requestFromServer(
         settings,