Add optional App Health endpoint telemetry

[sarthakagrawal927]

Summary

• Add the official App Health 0.4.0 Hono SDK from its immutable public release tarball.
• Mount opt-in endpoint summaries on Reader's API Worker. Collection stays disabled when APP_HEALTH_INGEST_KEY is absent or blank.
• Reuse a Worker-local client for one stable key/environment tuple and send delivery through Hono's ExecutionContext.waitUntil path.
• Test dynamic route normalization, omitted query/header/body values, disabled mode, response preservation, and client reuse.

No secret or production binding was added, and nothing was deployed.

Verification

• pnpm exec vitest run src/worker.test.ts src/worker/app-health.test.ts — passed (5 tests)
• pnpm typecheck — passed
• pnpm exec biome check on changed files — passed
• Pre-push lint hook — 0 errors, 38 existing warnings across 226 files

Closes #57

[cloudflare-workers-and-pages]

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	reader	e4dba19	Sep 28 2026, 11:00 PM