feat: add Xquik as X/Twitter search source

Add Xquik (xquik.com) as a new X/Twitter search source that uses a REST
API with full engagement metrics (likes, retweets, replies, quotes,
views, bookmarks). Uses stdlib urllib only -- no new dependencies.

- scripts/lib/xquik.py: source module with search, parse, query expansion
- tests/test_xquik.py: 32 unit tests covering all functions
- env.py: XQUIK_API_KEY config and availability check
- pipeline.py: source registration and retrieve dispatch
- normalize.py: reuses _normalize_x (same item format as Bird)

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

scripts/lib/normalize.py

@@ -46,6 +46,7 @@ def normalize_source_items(
         "bluesky": lambda s, i, idx, fd, td: _normalize_microblog(s, i, idx, fd, td, "BS", "Bluesky post"),
         "truthsocial": lambda s, i, idx, fd, td: _normalize_microblog(s, i, idx, fd, td, "TS", "Truth Social post"),
         "threads": lambda s, i, idx, fd, td: _normalize_microblog(s, i, idx, fd, td, "TH", "Threads post"),
+        "xquik": _normalize_x,
         "pinterest": _normalize_pinterest,
         "polymarket": _normalize_polymarket,
         "grounding": _normalize_grounding,