feat(cli): tree export-graph + demo recording for mindmap M1 (Refs ST-6)

[serenakeyitan]

Summary

Lands M1: Data export + demo recording for the live mindmap (parent: ST-4, engineer brief: ST-6, milestone: ST-9).

• New CLI: first-tree tree export-graph [--out graph.json] [--root .] [--repo owner/repo] — walks a Context Tree, parses NODE.md frontmatter (title / owners / tags / kind / soft_links), emits the v1 graph schema from ST-4 §2.1.
• Parent edges derive from the path hierarchy; link edges come from soft_links frontmatter and are dropped when the target node does not exist.
• Bundled demo at `apps/doc-website/public/demo/` (mirrored at `docs/public/demo/` so VitePress actually serves it):
  • `graph.json` (24 nodes, 26 edges — 4 domains, decisions, constraints)
  • `trace.jsonl` (128 navigation events, 4 agents, ~60s loop, matches the live-event shape in ST-4 §2.2)
  • `index.html` — standalone canvas + d3-force renderer; no live trace yet, no polish, as scoped for M1.
• Demo content is hand-crafted while the canonical demo tree (ST-7 PM deliverable) is in flight; regenerate with `apps/cli/scripts/generate-demo-{graph,trace}.mjs`.

Refs ST-6, ST-9.

Acceptance (from ST-9)

• `first-tree tree export-graph --out graph.json` ships at `apps/cli/src/commands/tree/export-graph.ts` with unit tests
• Output matches schema in ST-4 §2.1 (version, repo, nodes[], edges[])
• Bundled demo JSONL recording exists at `apps/doc-website/public/demo/trace.jsonl` (~60s loop, 4 agents, ≥120 events — actual: 128)
• Static graph renders in a throwaway page from `graph.json` (no live yet, no polish)
• PR opened against `dev` and links `Refs ST-6`

Test plan

• `pnpm --filter first-tree typecheck` clean
• `pnpm --filter first-tree test` — 125 passing (5 new `export-graph` tests)
• `pnpm --filter @first-tree/github-scan test` — 498 passing (unchanged)
• CLI smoke test: `node apps/cli/dist/index.js tree export-graph --help` shows the new options
• CLI smoke test: `node apps/cli/dist/index.js tree export-graph --root . --out /tmp/g.json` produces valid JSON against this very repo (39 nodes, 0 edges — expected, since this source repo is not itself a Context Tree)
• Open `apps/doc-website/docs/public/demo/index.html` in a browser via `pnpm --filter doc-website docs:dev` and confirm the static graph renders

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Project	Deployment	Actions	Updated (UTC)
first-tree-doc-website	Ready	Preview, Comment	May 12, 2026 10:54pm