chore: bootstrap agent-ready docs, rules and Bun workspace

Adds the approved v1 design spec, UI mockups, AGENTS.md (with CLAUDE.md
and GEMINI.md pointers), architecture/decisions/todo/permissions docs,
agent permission files, and an empty Bun workspaces skeleton.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/TODO.md

@@ -0,0 +1,26 @@
+# TODO
+
+Durable backlog. Agents append here instead of leaving `TODO` comments in source.
+Small, specific, independently actionable. Remove only when actually done.
+
+## Now
+- [ ] Choose a linter/formatter (e.g. Biome), then add `lint` to `package.json`, `AGENTS.md` and `docs/PERMISSIONS.md`.
+- [ ] Add CI on Gitea Actions: install, typecheck, and test on SQLite and Postgres. Add a guard that fails if `AGENTS.md` is over 150 lines.
+
+## Next
+- [ ] Phase 2 and Phase 3 plans (spec §12).
+
+## Someday
+
+## Recurring
+- [ ] Maintain `AGENTS.md`:
+  - **Add a rule only in response to a real failure.** When an agent repeatedly gets something wrong,
+    that is a gap; add one line, ideally with a code example. Do not pre-empt hypothetical mistakes.
+  - **Update in the same PR as the convention change.** A stale rules file is worse than none, because
+    it actively misleads.
+  - **Prune quarterly.** Delete rules whose convention has changed or whose mistake no longer occurs.
+  - **Optional, cheap validation:** run the same task twice in clean sessions, with and without the
+    file, and compare steps and token use.
+
+## Known issues
+- [ ] `bun run typecheck` fails with TS18003 until source files exist under `apps/`, `packages/` or `plugins/`.