feat: implement check-updates, job-backed ingest status, and dedup scan

Replace the four stub endpoints with real implementations, all requiring
an explicit tenant user (Phase B rule):

- /ingest/check-updates: GraphService now records a SHA-256 content_hash
  on every Document node at ingestion time; the endpoint compares those
  stored hashes against current Wiki.js page content in one UNWIND Cypher
  query per tenant and returns changed/new/deleted page lists (entity-stub
  pages excluded, pre-hash-tracking documents flagged stored_hash_missing).
- /ingest/status/{job_id}: backed by the Redis JobManager; jobs are
  tenant-scoped (foreign jobs 404). /ingest/page, /ingest/batch and
  /ingest/all now create job records and return job_id.
- /ingest/repo-status/{repository}: wiki page count vs indexed Document
  nodes under users/{tenant}/{repository} plus tenant job stats.
- /deduplicate/check: tenant-scoped Qdrant similarity scan; chunk pairs
  above ~0.9 cosine from different pages grouped per page pair with best
  score and page references (read-only).

Supporting changes: get_job_manager dependency (+ shutdown close),
scroll_all_points can return vectors, VectorService.find_duplicate_pairs,
src/core/hashing.compute_content_hash. 13 new offline unit tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QbFZyDvYksazX6nYQYZ67L

src/services/graph_service.py

@@ -452,14 +452,20 @@ class GraphService:
             user_base_label = get_neo4j_user_base_label(user)  # For entities
             user_doc_label = get_neo4j_user_label(user)  # For documents
 
-            # Create/update Document node
+            # Create/update Document node.
+            # content_hash records the fingerprint of the ingested content so
+            # /ingest/check-updates can detect changed pages without re-reading
+            # the graph's source content.
+            from src.core.hashing import compute_content_hash
+
             doc_query = f"""
             MERGE (d:{user_doc_label}:Document {{page_id: $page_id}})
             SET d.title = $title,
                 d.path = $path,
                 d.tags = $tags,
                 d.updated_at = datetime(),
-                d.content_length = $content_length
+                d.content_length = $content_length,
+                d.content_hash = $content_hash
             RETURN d
             """
 
@@ -468,7 +474,8 @@ class GraphService:
                 "title": page.get("title"),
                 "path": page.get("path"),
                 "tags": tags,
-                "content_length": len(content)
+                "content_length": len(content),
+                "content_hash": compute_content_hash(content)
             })
 
             nodes_created = 1  # Document node