feat: Add Dockerfile, preview config, and seed script for self-preview deployments

Containerize Codewalkers with a multi-stage Docker build (Node + Caddy) and
add a seed script that populates the database with a demo initiative, 3 phases,
9 tasks, 3 agents with JSONL log output, a root page, review comments, and a
git repo with real branch diffs for the review tab.

docs/preview.md

@@ -358,6 +358,47 @@ Polls `getPreviewStatus` with `refetchInterval: 3000` while active.
 - `GracefulShutdown` calls `previewManager.stopAll()` during shutdown
 - `requirePreviewManager(ctx)` helper in `apps/server/trpc/routers/_helpers.ts`
 
+## Codewalkers Self-Preview
+
+Codewalkers itself has a Dockerfile, `.cw-preview.yml`, and seed script for preview deployments. This lets you demo the full app — initiatives, phases, tasks, agents with output, pages, and review tab with real git diffs.
+
+### Files
+
+| File | Purpose |
+|------|---------|
+| `Dockerfile` | Multi-stage: deps → build (server+web) → production (Node + Caddy) |
+| `.cw-preview.yml` | Preview config: build, healthcheck, seed |
+| `scripts/Caddyfile` | Caddy config: SPA file server + tRPC reverse proxy |
+| `scripts/entrypoint.sh` | Init workspace, start backend, run Caddy |
+| `scripts/seed-preview.sh` | Create demo git repo + run Node.js seed |
+| `apps/server/preview-seed.ts` | Populate DB with demo initiative, phases, tasks, agents, log chunks, pages, review comments |
+
+### Container Architecture
+
+Single container running two processes:
+- **Node.js backend** on port 3847 (tRPC API + health endpoint)
+- **Caddy** on port 3000 (SPA file server, reverse proxy `/trpc` and `/health` to backend)
+
+### Seed Data
+
+The seed creates a "Task Manager Redesign" initiative with:
+- 3 phases (completed, pending_review, in_progress)
+- 9 tasks across phases
+- 3 agents with JSONL log output
+- Root page with Tiptap content
+- 3 review comments on the pending_review phase
+- Git repo with 3 branches and real commit diffs for the review tab
+
+### Manual Testing
+
+```sh
+docker build -t cw-preview .
+docker run -p 3000:3000 cw-preview
+# Wait for startup, then seed:
+docker exec <container> sh /app/scripts/seed-preview.sh
+# Browse http://localhost:3000
+```
+
 ## Dependencies
 
 - `js-yaml` + `@types/js-yaml` — for parsing `.cw-preview.yml`