chore: post-Phase-1 cleanup — gitignore, packaging, backlog

- .gitignore: add *.egg-info/ so editable installs don't show in git status.
- pyproject.toml: add [build-system] and [tool.setuptools.packages.find]
  scoped to chat*, fixing pip install -e . which was failing on data/
  auto-discovery.
- CLAUDE.md: add Phase 1.5 cleanup backlog section under Phase 1 status,
  capturing the small follow-ups surfaced in implementer reviews
  (open_db refactor, regenerate SSE broadcast, you-activity purge,
  drawer edits for deferred fields, NICE trim order).

pyproject.toml

@@ -19,6 +19,13 @@ dependencies = [
 [project.optional-dependencies]
 dev = ["pytest>=8", "pytest-asyncio>=0.23", "freezegun>=1.4"]
 
+[build-system]
+requires = ["setuptools>=61"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools.packages.find]
+include = ["chat*"]
+
 [tool.pytest.ini_options]
 pythonpath = ["."]
 asyncio_mode = "auto"