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.

Dockerfile

@@ -0,0 +1,48 @@
+# Stage 1: Install dependencies (native addons need build tools)
+FROM node:20-alpine AS deps
+RUN apk add --no-cache python3 make g++
+WORKDIR /app
+COPY package.json package-lock.json ./
+COPY apps/web/package.json apps/web/package.json
+COPY packages/shared/package.json packages/shared/package.json
+RUN npm ci
+
+# Stage 2: Build everything (web needs server types via packages/shared)
+FROM deps AS build
+COPY tsconfig.json ./
+COPY apps/server/ apps/server/
+COPY apps/web/ apps/web/
+COPY packages/shared/ packages/shared/
+# Server build (tsc → apps/server/dist/)
+RUN npm run build
+# Web build (vite bundle → apps/web/dist/)
+RUN npx --workspace=apps/web vite build
+
+# Stage 3: Production image
+FROM node:20-alpine AS prod
+RUN apk add --no-cache git curl jq
+COPY --from=caddy:2-alpine /usr/bin/caddy /usr/bin/caddy
+
+WORKDIR /app
+
+# Node modules (includes native better-sqlite3)
+COPY --from=deps /app/node_modules/ node_modules/
+COPY package.json ./
+
+# Server build output + drizzle migrations
+COPY --from=build /app/apps/server/dist/ apps/server/dist/
+COPY apps/server/drizzle/ apps/server/drizzle/
+
+# Web build output
+COPY --from=build /app/apps/web/dist/ apps/web/dist/
+
+# Scripts and config
+COPY scripts/ scripts/
+COPY scripts/Caddyfile /etc/caddy/Caddyfile
+RUN chmod +x scripts/*.sh
+
+# Workspace volume
+RUN mkdir -p /workspace
+
+EXPOSE 3000
+ENTRYPOINT ["sh", "/app/scripts/entrypoint.sh"]