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/src/refcurator/utils.py

@@ -0,0 +1,75 @@
+"""Common utilities for the reference curator pipeline."""
+
+from __future__ import annotations
+
+import hashlib
+import logging
+import re
+import unicodedata
+from urllib.parse import urlparse, urlunparse, parse_qs, urlencode
+
+
+def normalize_url(url: str) -> str:
+    """Normalize a URL for deduplication.
+
+    - Lowercase scheme and host
+    - Remove trailing slashes
+    - Sort query parameters
+    - Remove common tracking params (utm_*, ref, fbclid)
+    - Remove fragment
+    """
+    parsed = urlparse(url)
+    scheme = parsed.scheme.lower()
+    netloc = parsed.netloc.lower()
+    path = parsed.path.rstrip("/") or "/"
+
+    # Sort query params, removing tracking params
+    tracking_params = {"utm_source", "utm_medium", "utm_campaign", "utm_content",
+                       "utm_term", "ref", "fbclid", "gclid", "mc_cid", "mc_eid"}
+    params = parse_qs(parsed.query, keep_blank_values=True)
+    filtered = {k: v for k, v in sorted(params.items()) if k not in tracking_params}
+    query = urlencode(filtered, doseq=True)
+
+    return urlunparse((scheme, netloc, path, "", query, ""))
+
+
+def url_hash(url: str) -> str:
+    """SHA-256 hash of normalized URL. Matches the url_hash column in schema.sql."""
+    return hashlib.sha256(normalize_url(url).encode()).hexdigest()
+
+
+def slugify(text: str) -> str:
+    """Convert text to a URL/folder-friendly slug.
+
+    >>> slugify("Prompt Engineering Best Practices")
+    'prompt-engineering-best-practices'
+    """
+    text = unicodedata.normalize("NFKD", text)
+    text = text.encode("ascii", "ignore").decode()
+    text = text.lower()
+    text = re.sub(r"[^a-z0-9]+", "-", text)
+    text = text.strip("-")
+    return text or "untitled"
+
+
+def count_tokens(text: str) -> int:
+    """Approximate token count using chars/4 heuristic.
+
+    Good enough for compression ratio calculations without requiring tiktoken.
+    """
+    return max(1, len(text) // 4)
+
+
+def setup_logging(level: str = "INFO", run_id: int | None = None) -> logging.Logger:
+    """Configure and return a logger for the reference curator pipeline."""
+    logger = logging.getLogger("refcurator")
+    if not logger.handlers:
+        handler = logging.StreamHandler()
+        fmt = "[refcurator]"
+        if run_id:
+            fmt += f" [run:{run_id}]"
+        fmt += " %(levelname)s: %(message)s"
+        handler.setFormatter(logging.Formatter(fmt))
+        logger.addHandler(handler)
+    logger.setLevel(getattr(logging, level.upper(), logging.INFO))
+    return logger