First slice of making Claude's session store the source of truth. Adds a reader
(api/chat/claude-sessions.ts) that lists sessions straight from Claude's JSONL
transcripts under $HOME/.claude/projects/<cwd-slug>/, plus GET /chat/sessions
over a dedicated per-user claude_sessions working directory. No bookkeeping
layer — Claude's files are authoritative. Verified against real transcripts.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
