Simplify auth and search client, drop local JWT expiry tracking

Auth:
- Remove jwt.ts — stop decoding JWT exp claims locally
- Simplify OTP login: direct token extraction from verify response,
  remove CookieJar, BFS token extraction, session fallback, CF bypass
- Storage: drop expires field, store token-only; clear on 401/403
- Single auth path: try stored token → macOS app → OTP fallback

Search client:
- Remove Cloudflare subprocess fallback (fetchViaBunRuntime)
- Remove streamFromText, isCloudflareChallenge, BunFetchResult
- Simplify SSE fetch to single fetch() call with abort signal
- Let server validate tokens; clear cache on auth errors

Render:
- Extract shared utilities (asString, truncate) to render/util.ts
- Simplify call.ts and result.ts to import from shared module

Tests:
- Remove jwt.test.ts (module deleted)
- Add otp-flow.test.ts for email OTP authentication
- Simplify login and client tests for reduced code paths

Add debug scripts and plan documents.

src/commands/login.ts

@@ -3,6 +3,7 @@ import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
 import { authenticate } from "../auth/login.js";
 import { clearToken } from "../auth/storage.js";
 import { AuthError } from "../search/types.js";
+import { errorMessage } from "../render/util.js";
 
 const LOGIN_COMMAND_NAME = "perplexity-login";
 
@@ -110,7 +111,7 @@ export function registerPerplexityCommands(pi: ExtensionAPI): void {
           return;
         }
 
-        ctx.ui.notify(`Perplexity login failed: ${(error as Error).message || "Unknown error"}`, "error");
+        ctx.ui.notify(`Perplexity login failed: ${errorMessage(error)}`, "error");
       }
     },
   });