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/services/plugin_context.py

@@ -25,7 +25,7 @@ from scribe.services import knowledge as knowledge_svc
 from scribe.services import notes as notes_svc
 from scribe.services import projects as projects_svc
 from scribe.services import rulebooks as rulebooks_svc
-from scribe.services.access import label_shared_items
+from scribe.services.access import label_shared_items, owner_names_for
 from scribe.services.embeddings import semantic_search_notes
 from scribe.services.retrieval_telemetry import record_retrieval
 from scribe.services.settings import get_setting
@@ -196,6 +196,11 @@ async def build_autoinject_hint(
         threshold=cfg["threshold"],
         project_id=(project_id or None),
         exclude_ids=set(exclude_ids or []),
+        # Injection is the one retrieval nobody asked for, so it takes the BROWSE
+        # scope: never a record shared one-to-one with the operator. What can
+        # still appear is a collaborator's note inside a shared project — legible
+        # only because the line below names its owner.
+        scope="browse",
     )
     record_retrieval(
         user_id=user_id, source="auto_inject", query=q,
@@ -210,6 +215,13 @@ async def build_autoinject_hint(
     top_score = hits[0][0]
     kept = [(s, n) for s, n in hits if s >= top_score - _AUTOINJECT_BAND]
 
+    # A collaborator's note can reach this menu via a shared project, and the
+    # operator never asked for it — so say whose it is. Unattributed, it reads as
+    # something they wrote and settled.
+    owners = await owner_names_for({
+        int(n.user_id) for _s, n in kept if n.user_id != user_id
+    })
+
     lines = [
         "> Possibly relevant from your Scribe notes — call `get_note(id)` to "
         "open any in full (titles only; injected once per session):",
@@ -218,7 +230,11 @@ async def build_autoinject_hint(
     for score, note in kept:
         note_ids.append(int(note.id))
         title = (note.title or "(untitled)").replace("\n", " ").strip()
-        lines.append(f"> - #{note.id} \"{title}\" ({score:.2f})")
+        line = f"> - #{note.id} \"{title}\" ({score:.2f})"
+        if note.user_id != user_id:
+            who = owners.get(int(note.user_id)) or "another user"
+            line += f" — shared by {who}, treat as a suggestion"
+        lines.append(line)
 
     return {"context": "\n".join(lines), "note_ids": note_ids, "config": cfg}