Add document preview, delete, and fix scroll in documents panel

Documents tab was limited to ~9 visible items due to fixed max-height
without overflow-hidden. Now uses 70vh with proper overflow. Added
click-to-preview (shows extracted text in dialog) and delete button
with confirmation dialog + backend DELETE endpoint.

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

mcp-server/src/legal_mcp/services/db.py

@@ -747,6 +747,22 @@ async def update_decision(decision_id: UUID, **fields) -> None:
         await conn.execute(sql, decision_id, *values)
 
 
+# ── Document deletion ──────────────────────────────────────────────
+
+async def delete_document(doc_id: UUID) -> bool:
+    """Delete a document and all its chunks. Returns True if deleted."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        async with conn.transaction():
+            await conn.execute(
+                "DELETE FROM document_chunks WHERE document_id = $1", doc_id
+            )
+            result = await conn.execute(
+                "DELETE FROM documents WHERE id = $1", doc_id
+            )
+            return int(result.split()[-1]) > 0
+
+
 # ── Chunks & Vectors ───────────────────────────────────────────────
 
 async def delete_document_chunks(document_id: UUID) -> int: