fix(auth): stop infinite SSE retry on 401/403, surface auth failures (#79)

* fix(auth): stop infinite SSE retry on 401/403 and surface auth failures

Root cause (Sentry OPENCODE-MOBILE-1, 309 events / 65 users): auth is static
HTTP Basic and no code path treated 401 specially. The SSE reconnect loop in
events.ts retried on a fixed backoff regardless of cause, so a bad password
spammed Sentry and drained battery forever with zero user feedback.
Advanced-mode connection save also had no pre-flight check and silently
persisted bad credentials as the active connection.

- src/lib/api-error.ts: new pure ApiAuthError/isAuthStatus/isAuthError module
  (node --test covered) so 401/403 are distinguishable from other failures.
- src/lib/sdk.ts: request()/events() now throw ApiAuthError for 401/403
  instead of a generic Error.
- src/stores/events.ts: the SSE loop stops retrying on an auth error and sets
  a new `authError` flag instead of reconnecting forever; other errors keep
  the existing backoff. Fires connection_failed (source: sse, error_class:
  unauthorized) so it's visible in the existing funnel.
- app/(tabs)/index.tsx: sessions screen shows an "Authentication Failed"
  state with a link to the connection edit screen when authError is set.
- app/connection/[id].tsx: saving edited credentials for the active
  connection now reconnects SSE immediately instead of requiring an app
  restart.
- app/connection/add.tsx: Advanced-mode save now runs the same testConnection
  pre-flight as Quick Connect and shows the same "Connection Failed" alert
  (with diagnostics/share-report) instead of silently saving bad credentials.

Closes #76

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NJKAQ6HAikWGQK7PGZ5Y4E

* fix(auth): add Retry button on 401 error state, widen ConnectionTestSource

- Authentication Failed screen now offers Retry alongside Check
  Credentials, calling events store's connect() directly to restart
  the SSE state machine on transient 401s without leaving the app.
- Widen ConnectionTestSource to include 'sse' (events.ts:389's
  connection_failed track call) and note the activation funnel only
  filters on source=onboarding.

Addresses PR #79 review follow-ups.

---------

Co-authored-by: engineer <engineer@gray-knight-m1.local>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/lib/sdk.ts

@@ -5,6 +5,9 @@
 import { fetch as expoFetch } from "expo/fetch"
 import { buildRequestHeaders } from "./headers"
 import { SSEParser } from "./sse"
+import { apiErrorFor } from "./api-error"
+
+export { ApiAuthError, isAuthError } from "./api-error"
 
 export interface ClientConfig {
   baseUrl: string
@@ -196,7 +199,7 @@ async function request<T>(config: ClientConfig, path: string, options: RequestIn
 
   if (!response.ok) {
     const error = await response.text()
-    throw new ApiError(response.status, error)
+    throw apiErrorFor(response.status, `API Error: ${response.status} - ${error}`)
   }
 
   return response.json()
@@ -243,7 +246,7 @@ export function createClient(config: ClientConfig) {
         // Must use expo/fetch for ReadableStream support on native
         const response = await expoFetch(url, { headers, signal })
         if (!response.ok || !response.body) {
-          throw new Error(`Failed to connect to event stream: ${response.status}`)
+          throw apiErrorFor(response.status, `Failed to connect to event stream: ${response.status}`)
         }
 
         const reader = response.body.getReader()