fix(ci): run full pytest suite, repair 13 rotted tests

CI was running only test_plugin_contract.py and test_version_consistency.py
(2 of 84 test files), masking 13 rotted tests across 4 clusters. The suite is
fully offline-safe (1402 tests in ~7s without network), so the narrow scope
wasn't gating integration flakiness; it was just stale. validate.yml now runs
`uv run pytest` against the full suite.

Engine fix: store.findings_from_report is rerank-first. ranked_candidates is
the primary persistence path; hackernews/polymarket are unconditionally
supplemented from items_by_source because they rank poorly but matter for
watchlists. When ranked_candidates was empty (rerank failed or skipped),
reddit, x, and every other source were silently dropped. The supplement loop
now falls back to all sources only when ranked_candidates is empty; the normal
path is unchanged.

Test repairs:
- test_store.py (6) + test_watchlist_commands.py (2): cascade from the engine fix
- test_get_new_findings_filters_by_date (latent): local-time vs SQLite UTC
  flake — switched to datetime.now(timezone.utc)
- TestPollDeviceAuth (3): mock_time.time side_effect lists too short after
  impl added a last_reminder call — padded timeout test, pinned others to
  return_value=0 (loops terminate via urlopen, not the clock)
- test_bare_run_emits_web_promo: engine reads ~/.config/last30days/.env, so
  a contributor's saved EXA/PARALLEL key made grounding "available" and
  suppressed the web promo. Also missing X made the "x" promo preempt "web".
  Set LAST30DAYS_CONFIG_DIR="", subprocess cwd=tmpdir, XAI_API_KEY stub.

tests/test_store.py

@@ -3,7 +3,7 @@
 import json
 import sqlite3
 import tempfile
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from pathlib import Path
 
 import pytest
@@ -503,16 +503,16 @@ def test_get_new_findings_filters_by_date(temp_db, sample_report):
     findings = store.findings_from_report(sample_report)
     store.store_findings(run_id, topic["id"], findings)
     
-    # Get findings since tomorrow (should be empty)
-    tomorrow = (datetime.now() + timedelta(days=1)).strftime("%Y-%m-%d")
+    # Use UTC because store writes first_seen via SQLite's datetime('now') (UTC).
+    # Local-time math here would flake near midnight UTC.
+    tomorrow = (datetime.now(timezone.utc) + timedelta(days=1)).strftime("%Y-%m-%d")
     new_findings = store.get_new_findings(topic["id"], since=tomorrow)
-    
+
     assert len(new_findings) == 0
-    
-    # Get findings since yesterday (should have all)
-    yesterday = (datetime.now() - timedelta(days=1)).strftime("%Y-%m-%d")
+
+    yesterday = (datetime.now(timezone.utc) - timedelta(days=1)).strftime("%Y-%m-%d")
     new_findings = store.get_new_findings(topic["id"], since=yesterday)
-    
+
     assert len(new_findings) == 4