feat(reference-curator): implement Python scripts + Gemini quality gate

Build the refcurator shared Python package and 7 CLI scripts that were
previously specification-only. Add Gemini CLI as an independent pre-distillation
quality evaluator, replacing the circular Claude-self-review pattern.

Key changes:
- shared/lib/src/refcurator/: 7-module package (config, db, models, utils,
  manifest, gemini) with PyMySQL + JSON file dual backend
- 7 Click CLI scripts: discover, crawl_mgr, repo, distiller, reviewer,
  exporter, pipeline — each with subcommands for data management
- Gemini quality gate: evaluates raw content BEFORE distillation using
  5 criteria (relevance, authority, completeness, freshness, distill_value)
- Pipeline reordered: discovery → crawl → store → evaluate → distill → export
- Bug fixes from Codex adversarial review:
  - FileBackend now hard-fails on JOIN/aggregate/GROUP BY queries
  - Exporter uses MAX(review_id) to prevent shipping stale approvals
  - Distiller updates existing rows on refactor instead of forking
- Updated all 7 CLAUDE.md directives with real script references
- install.sh updated with refcurator package install step

51/51 E2E tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

custom-skills/90-reference-curator/shared/lib/pyproject.toml

@@ -0,0 +1,34 @@
+[project]
+name = "refcurator"
+version = "1.0.0"
+description = "Reference Curator — data management for the reference curation pipeline"
+requires-python = ">=3.12"
+license = "MIT"
+authors = [
+    { name = "Andrew Yim", email = "andrew@ourdigital.org" },
+]
+dependencies = [
+    "pymysql>=1.1.0",
+    "click>=8.0",
+    "pydantic>=2.0",
+    "pyyaml>=6.0",
+    "rich>=13.0",
+    "python-dotenv>=1.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "ruff>=0.4",
+]
+
+[build-system]
+requires = ["setuptools>=68.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.ruff]
+line-length = 100
+target-version = "py312"