feat(precedents): UI button queues extraction for local MCP worker

The chair wanted a one-click "extract metadata" button on the edit sheet.
The constraint stays the same — claude_session needs the local CLI which
the container doesn't have, so the button can't run the extractor itself.
Compromise: button stamps a queue marker; the local MCP server drains the
queue on demand.

DB (V8): two nullable timestamps on case_law,
metadata_extraction_requested_at and halacha_extraction_requested_at,
with partial indexes for cheap "find pending" scans.

API:
  POST /api/precedent-library/{id}/request-metadata   → stamp the row
  POST /api/precedent-library/{id}/request-halachot   → same for halacha
  GET  /api/precedent-library/queue/pending?kind=...  → read-only view

UI: Sparkles button in the edit sheet header. Click → toast tells the
chair what to run from Claude Code. The button never triggers the
extractor directly from the container.

MCP tool: precedent_process_pending(kind, limit) — runs from Claude Code
with the local CLI, picks up everything stamped, calls the extractor for
each, clears the timestamp on success. Failures keep the timestamp so the
next invocation retries them.

Architectural rule (claude_session local-only) is preserved end-to-end
and called out in the new endpoint comment + tool docstring.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/tools/precedent_library.py

@@ -140,7 +140,7 @@ async def precedent_extract_halachot(case_law_id: str) -> str:
 
 
 async def precedent_extract_metadata(case_law_id: str) -> str:
-    """חילוץ מטא-דאטה (case_name קצר, summary, headnote, key_quote, subject_tags, appeal_subtype) מהטקסט. ממלא רק שדות ריקים — לא דורס מה שכבר הוזן."""
+    """חילוץ מטא-דאטה (case_name קצר, summary, headnote, key_quote, subject_tags, appeal_subtype, date, level, court, source_type) מהטקסט. ממלא רק שדות ריקים — לא דורס מה שכבר הוזן."""
     try:
         cid = UUID(case_law_id)
     except ValueError:
@@ -152,6 +152,23 @@ async def precedent_extract_metadata(case_law_id: str) -> str:
     return _ok(result)
 
 
+async def precedent_process_pending(kind: str = "metadata", limit: int = 20) -> str:
+    """ריקון תור בקשות חילוץ שנערמו ע"י כפתורי ה-UI. kind: 'metadata' או 'halacha'.
+
+    הכפתור ב-UI מסמן ב-DB שהפסיקה מבקשת חילוץ. כלי זה (שרץ מקומית עם CLI)
+    סורק את התור ומריץ את ה-extractor לכל פריט. אחרי הצלחה הסימון מתנקה.
+    """
+    if kind not in {"metadata", "halacha"}:
+        return _err("kind חייב להיות 'metadata' או 'halacha'")
+    try:
+        result = await precedent_library.process_pending_extractions(
+            kind=kind, limit=limit,
+        )
+    except Exception as e:
+        return _err(str(e))
+    return _ok(result)
+
+
 async def search_precedent_library(
     query: str,
     practice_area: str = "",