feat(acl): unify the retrieval scopes; mark shared rows in Knowledge browse

Closes #2092 and the Knowledge-browse provenance gap.

The two halves of a hybrid search disagreed: the keyword half honoured shares
while the semantic half was pinned to NoteEmbedding.user_id, so a shared record
was findable by wording and invisible by meaning — the case a semantic search
exists to serve. semantic_search_notes now scopes on Note via a `scope`
parameter, and each of its five callers declares which kind of act it is:

  mcp/tools/search.py     read    the agent asked
  routes/search.py        read    the user typed it
  knowledge.py (semantic) read    matches the keyword half beside it
  plugin_context.py       browse  nobody asked; never a one-to-one share
  dedup.py                own     a verdict that blocks a write must not hinge
                                  on another person's notes

That last one is the reason this isn't a single global widening: the dedup gate
returns "update the existing one instead", so matching a stranger's record would
refuse a legitimate create and point at something the caller can't edit. Scope
defaults to "own" so a caller that forgets is wrong in the safe direction, and an
unknown scope raises rather than falling back — a typo there would be a
data-exposure bug.

Auto-inject keeps the browse scope, which still admits a collaborator's note via
a shared project. Its menu line is the only provenance an agent sees, so a
foreign hit now reads: #12 "Title" (0.71) - shared by alex, treat as a
suggestion. MCP and REST search results carry shared/owner too.

Knowledge browse: the feed hydrates cards from /api/knowledge/batch rather than
the list route, so both paths label rows now, and KnowledgeView shows "by
<owner>" on records the viewer doesn't own.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLwAaV4DQEmVyn496HnEvt

src/scribe/routes/knowledge.py

@@ -5,6 +5,7 @@ from quart import Blueprint, jsonify, request
 
 from scribe.auth import get_current_user_id, login_required
 from scribe.routes.utils import parse_pagination
+from scribe.services.access import label_shared_items
 
 logger = logging.getLogger(__name__)
 
@@ -54,7 +55,9 @@ async def list_knowledge():
     )
 
     return jsonify({
-        "items": items,
+        # Mark rows another user owns: this feed can be mixed-ownership, and an
+        # unmarked card reads as one the viewer wrote.
+        "items": await label_shared_items(uid, items),
         "total": total,
         "page": page,
         "per_page": limit,
@@ -116,7 +119,9 @@ async def get_knowledge_batch():
 
     from scribe.services.knowledge import get_knowledge_by_ids
     items = await get_knowledge_by_ids(uid, ids)
-    return jsonify({"items": items})
+    # The scrolling feed hydrates its cards here, not from the list route, so the
+    # ownership markers have to be applied on this path too.
+    return jsonify({"items": await label_shared_items(uid, items)})
 
 
 @knowledge_bp.route("/tags", methods=["GET"])