fix(docker): add git, ca-certificates, and ripgrep to production image

Agent mode requires git for mirror cloning and rg for code search.
Both were missing from oven/bun:1-slim causing command failures (exit code -1).

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Dockerfile

@@ -28,6 +28,8 @@ COPY tsconfig.json .
 # ---- Stage 3: Production ----
 FROM oven/bun:1-slim
 
+RUN apt-get update && apt-get install -y --no-install-recommends git ca-certificates ripgrep && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 COPY --from=backend-builder /app/node_modules ./node_modules