fix: stop rewriting the wiki every run (hash excludes Last Updated timestamp) (#35)

## Bug (in prod)
`update_wiki_page` hashes the full wiki content, which begins with
`**Last Updated:** <current time>` (`build_wiki_content`). Because the
timestamp changes every run, `content_hash` is always new, `cached_hash
== content_hash` is never true, and the page is **rewritten with a fresh
revision every ~10 min even when nothing changed**. The entire
`wiki_hash_cache` table is dead weight.

**Impact:** needless Reddit wiki writes + revision-history spam. Not
data corruption.

## Fix
`get_content_hash` strips the volatile `Last Updated` line before
hashing, so the change-detection hash reflects only the modlog body.
Self-heals after one write post-deploy.

## Verification
- timestamp-only diff → identical hash (skip now works) ✓
- body change → different hash (still writes) ✓
- existing test suite passes (no regression)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Wiki updates now skip unchanged content more reliably, reducing
unnecessary edits.
* Continuous and forced refresh flows are more consistent when
rebuilding wiki pages.

* **Bug Fixes**
* Improved handling of wiki size limits and API errors for more reliable
updates.
* Better formatting and cleanup of moderation entries, including
timestamps and removal reasons.
  * Faster and more dependable data lookup during wiki generation.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: bakerboy448

modlog_wiki_publisher.py

@@ -366,8 +366,15 @@ def setup_database():
 
 
 def get_content_hash(content: str) -> str:
-    """Calculate SHA-256 hash of content"""
-    return hashlib.sha256(content.encode("utf-8")).hexdigest()
+    """Calculate SHA-256 hash of content for wiki change-detection.
+
+    Excludes the volatile ``**Last Updated:** <timestamp>`` header line so an
+    unchanged modlog produces a stable hash. Hashing the timestamped content
+    made every run differ, defeating the wiki_hash_cache skip and rewriting the
+    wiki page (a fresh revision) on every cycle even when nothing changed.
+    """
+    hashable = re.sub(r"^\*\*Last Updated:\*\* .*\n", "", content, count=1)
+    return hashlib.sha256(hashable.encode("utf-8")).hexdigest()
 
 
 def get_cached_wiki_hash(subreddit: str, wiki_page: str) -> Optional[str]: