feat(app): landing page + inspector (trace input, timeline, failures, report export)

[sepehr-safari]

Summary

Builds the landing page and the Inspector UI — the two flagship web features for v0.1.0.

Closes #27, Closes #28

Changes

Landing page (/)

• Hero: tagline + description + CTA (Try Inspector, View on GitHub)
• Features: inspect, detect, test, report
• What it's not: not a CSMS, not a simulator, not a compliance tool
• Architecture: package cards (core, scenarios, reporter, cli)
• Quick start: CLI commands
• Footer: GitHub, npm, docs, license

Inspector (/inspector)

• Trace input: paste textarea, file upload (with size limit), sample scenario selector
• Session timeline: clickable events with message type, action, timestamp, direction
• Message inspector: raw message JSON, normalized fields, payload
• Failure summary: severity emoji, description, suggested steps
• Report export: download Markdown report via Blob
• States: loading, empty, error (with non-sensitive messages)
• Browser-local: all parsing happens client-side, no network calls with trace data

Security

• No dangerouslySetInnerHTML — all rendering is React-safe
• File size limit enforced (10 MB)
• Input validation via Zod schemas in core package
• No auto-upload of trace data
• Non-sensitive error messages

Verification

• pnpm lint — ✅
• pnpm typecheck — ✅
• pnpm test — ✅ (196 tests)
• pnpm build — ✅ (all routes prerendered)
• pnpm format:check — ✅