feat(tiktok): add TikTok as 7th signal source via Apify

Add TikTok search, scoring, and rendering using the Apify platform
(clockworks/tiktok-scraper actor). Users bring their own APIFY_API_TOKEN
($5/month free credits, no CC required). The shared apify_client_wrapper
module is designed for reuse by future Facebook/Instagram sources.

- New modules: tiktok.py (search + caption extraction), apify_client_wrapper.py
- Schema: TikTokItem dataclass, shares field on Engagement, Report.tiktok
- Pipeline: normalize → filter → score → sort → dedupe → cross-link → render
- Scoring: 0.50*log1p(views) + 0.30*log1p(likes) + 0.20*log1p(comments)
- SKILL.md bumped to v2.7 with TikTok stats, citations, and security docs
- 26 unit tests covering relevance, normalize, score, dedupe, render, round-trip

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/lib/dedupe.py

@@ -45,7 +45,7 @@ def jaccard_similarity(set1: Set[str], set2: Set[str]) -> float:
     return intersection / union if union > 0 else 0.0
 
 
-AnyItem = Union[schema.RedditItem, schema.XItem, schema.YouTubeItem,
+AnyItem = Union[schema.RedditItem, schema.XItem, schema.YouTubeItem, schema.TikTokItem,
                 schema.HackerNewsItem, schema.PolymarketItem, schema.WebSearchItem]
 
 
@@ -57,6 +57,8 @@ def get_item_text(item: AnyItem) -> str:
         return item.title
     elif isinstance(item, schema.YouTubeItem):
         return f"{item.title} {item.channel_name}"
+    elif isinstance(item, schema.TikTokItem):
+        return f"{item.text} {item.author_name}"
     elif isinstance(item, schema.PolymarketItem):
         return f"{item.title} {item.question}"
     elif isinstance(item, schema.WebSearchItem):
@@ -74,6 +76,8 @@ def _get_cross_source_text(item: AnyItem) -> str:
     """
     if isinstance(item, schema.XItem):
         return item.text[:100]
+    if isinstance(item, schema.TikTokItem):
+        return item.text[:100]
     if isinstance(item, schema.HackerNewsItem):
         title = item.title
         if title.startswith("Show HN:"):
@@ -194,6 +198,14 @@ def dedupe_youtube(
     return dedupe_items(items, threshold)
 
 
+def dedupe_tiktok(
+    items: List[schema.TikTokItem],
+    threshold: float = 0.7,
+) -> List[schema.TikTokItem]:
+    """Dedupe TikTok items."""
+    return dedupe_items(items, threshold)
+
+
 def dedupe_hackernews(
     items: List[schema.HackerNewsItem],
     threshold: float = 0.7,