fix(oauth+errors): OAuth silent refresh, quota STOP patterns, compaction loop cap

Bug fixes:
1. OAuth token refresh (#3149): buildHttpRequestInit() now attempts silent refresh
   via refresh_token before triggering full browser re-auth. Added refresh() method
   to McpOAuthProvider. Includes test isolation fix for discovery mock.

2. Quota error STOP (#3126): Added STOP_MESSAGE_PATTERNS in model-error-classifier
   that take precedence over RETRYABLE_MESSAGE_PATTERNS. Message-only quota errors
   now non-retryable. Runtime-fallback: quota_exceeded with 'retrying in' signal
   still triggers fallback (provider-managed auto-retry). Restored removed patterns.

3. Compaction loop (#3127): MAX_RECOVERY_ATTEMPTS=3 cap + additional suppression
   guard from opencode session in degradation monitor.

Also: refactored extractAutoRetrySignal to auto-retry-signal.ts, new regression
tests for quota classifier and compaction degradation monitor.

src/shared/model-error-classifier.test.ts

@@ -215,6 +215,28 @@ describe("model-error-classifier", () => {
     //#then
     expect(result).toBe(true)
   })
+
+  test("treats subscription quota message as non-retryable", () => {
+    //#given
+    const error = { message: "Subscription quota exceeded. You can continue using free models." }
+
+    //#when
+    const result = shouldRetryError(error)
+
+    //#then
+    expect(result).toBe(false)
+  })
+
+  test("treats HTTP 429 rate limit message as retryable", () => {
+    //#given
+    const error = { message: "429 Too Many Requests: rate limit reached" }
+
+    //#when
+    const result = shouldRetryError(error)
+
+    //#then
+    expect(result).toBe(true)
+  })
 })
 
 export {}