fix: Dockerfile — all build and runtime issues

Sequential build failures fixed:
1. uv run playwright install chromium → playwright not in pyproject.toml/venv
   Fix: npm install -g @playwright/cli playwright && playwright install chromium
   Also installs @playwright/cli (the browser CLI used by research agents)

2. uv pip install amplifierd → package not on PyPI
   Fix: uv pip install --system from github.com/microsoft/amplifierd
   Also installs amplifier-foundation (also not on PyPI, git-only dep)
   Uses uv (not plain pip) to respect [tool.uv.sources] resolution

3. COPY frontend/dist/ → dist is gitignored, breaks fresh-clone builds
   Fix: build the frontend inside Docker using the installed Node.js
   (npm ci + npm run build); removes the pre-built dist assumption

Other fixes:
- Add git to apt-get (required for pip/uv git+https installs)
- Fix entrypoint.sh: amplifierd uses 'serve' subcommand and NAME=URI
  bundle format — was: amplifierd --port ... --bundle /path
  now: amplifierd serve --port ... --bundle name=/path --default-bundle name
- Add .dockerignore to exclude node_modules, .venv, dist, .git, etc.
  (keeps build context small and avoids stale artifacts in COPY steps)

.dockerignore

@@ -0,0 +1,14 @@
+**/__pycache__
+**/*.pyc
+**/*.egg-info
+.venv
+backend/.venv
+frontend/node_modules
+frontend/dist
+artifacts
+.git
+.gitea
+.pytest_cache
+.ruff_cache
+tests
+*.swp