Add CI/CD: Dockerfile + Gitea Actions workflow

- Multi-stage Dockerfile with Bun 1.3.6
- Gitea Actions workflow for auto-build
- Push to git.fuq.tv container registry
- Build cache optimization

Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,23 @@
+# AiWorker Backend - Docker Image
+FROM oven/bun:1.3.6-alpine AS base
+WORKDIR /app
+
+# Install dependencies
+FROM base AS install
+RUN mkdir -p /temp/prod
+COPY package.json bun.lockb /temp/prod/
+RUN cd /temp/prod && bun install --frozen-lockfile --production
+
+# Copy source
+FROM base AS release
+COPY --from=install /temp/prod/node_modules node_modules
+COPY . .
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=40s --retries=3 \
+  CMD bun fetch http://localhost:3000/api/health || exit 1
+
+# Run
+USER bun
+EXPOSE 3000
+ENTRYPOINT [ "bun", "src/index.ts" ]