Add theming system design plan

Fix lexicon convention issues identified in code review:
- Use knownValues (not implicit enum) for colorScheme field
- Wrap theme references with strongRef for CID integrity checks
- Separate themePolicy into its own singleton to prevent forum record bloat
- Note that forum.theme must be added to CLAUDE.md ownership list

Add missing implementation details:
- Elevate CSS sanitization from open question to mandatory Phase 3 gate
- Document cache key must include resolved color scheme
- Constrain fontUrls to HTTPS with allowlist consideration
- Add database schema notes for themes and memberships tables
- Clarify AppView endpoints are REST, not XRPC

Updates theme resolution waterfall to show CID integrity checks via strongRef.

Replace the single active-theme model with a full theme policy system:
- Admin curates available themes with separate light/dark defaults
- Users can pick their own theme from the available list
- Theme resolution waterfall: user pref → color scheme → forum default → fallback
- New themePolicy on forum.forum, preferredTheme on membership
- AppView API endpoints for theme CRUD and user preference
- Updated presets to ship light+dark variants
- 5-phase implementation plan reflecting new scope

https://claude.ai/code/session_01Y3xoFe9ty2gduA4KHVKeYx

Plan for a phpBB-inspired admin-customizable theme system with a
neobrutal default. Covers CSS custom property architecture, design
token schema, lexicon for theme storage on Forum DID, admin editor
workflow, and built-in preset themes. Scoped as post-MVP work.

https://claude.ai/code/session_01Y3xoFe9ty2gduA4KHVKeYx

Two options for running Postgres locally:

1. Docker Compose: `docker compose up -d` starts a PostgreSQL 17
container on port 5432 with persistent volume storage.

2. Devenv: `devenv up` now also starts a managed PostgreSQL 17 service
alongside the appview and web dev servers.

Both use the same credentials (atbb/atbb) and database name (atbb),
matching the existing DATABASE_URL in .env.example.

https://claude.ai/code/session_01T1qT4qo8eoui9X7f32PVt4

Use Node 22+ native --env-file=../../.env in dev/spike scripts so
packages pick up root .env variables without a dotenv dependency.
Also add devenv, direnv, and pre-commit entries to .gitignore.

Documents architecture, dev setup, lexicon conventions, AT Protocol
patterns, TypeScript/Hono gotchas, and git conventions.

Mark lexicon definitions and project scaffolding as complete, with
result notes. Spike script is written but awaiting PDS credentials.

Set up Turborepo monorepo with pnpm workspaces and devenv for the atBB
decentralized forum project. Defines 5 new AT Proto lexicon schemas
(category, role, membership, reaction, modAction) alongside the 3
existing ones, with a YAML→JSON→TypeScript build pipeline. Scaffolds
the Hono AppView API server, HTMX web UI server, and PDS spike script.