feat(telemetry): a usage event records which project the reader was in (#4196, #3735)

`RetrievalLog` has carried `project_id` since it existed, so "this record
was SURFACED on project B" was always answerable. `note_usage_events`
had none, so "this record was OPENED on project B" was not — and the two
cannot be joined to recover it, because there is deliberately no session
identity server-side. NoteUsageEvent's own docstring rules that out.

That gap sat exactly on the question milestone 385 exists to answer. A
lesson's whole claim is that it reaches a session on a project it was not
written on, and step 8's acceptance is "retrieved on a different project
AND opened". Each half was answerable; the conjunction was not.

WHICH project, because the name is ambiguous and the wrong reading makes
the column useless: it is the project the READER was in, never the one
the record belongs to. The record's own project is already on the note;
copying it here would answer a question nobody asked while looking like
it answered this one.

The surfacing half is free — every arm already holds the scope it just
searched, so auto_inject, lesson_slot, the write-path arms and
enter_project now record it. process_skill_sync does not and should not:
it installs every Process the operator can reach, which is not a
project-scoped question, so a project there would be a fiction.

The pull half needs the caller, since a getter knows only what it was
handed. The five single-record getters take `project_id: int = 0` and
pass it through, following the convention `search` and `create_*`
already set. Null stays an ordinary answer meaning "not reported" — a
pull with no project is still a pull and still counts toward dead
weight; it simply cannot speak to transfer. The four REST detail views
report none for now: a human opening a record in a browser is a
different event from an agent recalling one, and #2245 left that
asymmetry deliberately undecided.

Guarded the way #2245 and #2476 taught: by source inspection, because a
parameter that was never threaded through changes no return value and
shows up only as a column that is mysteriously always null. Three
guards — the signature, the pass-through, and the arms — plus the
can-fail test rule 167 asks for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

src/scribe/services/plugin_context.py

@@ -872,6 +872,7 @@ async def _reserve_slot_for_lesson(
     if slot_id not in already:
         record_surfaced(
             user_id=user_id, note_ids=[slot_id], source="lesson_slot",
+            project_id=project_id,
         )
     return kept + slot, slot_id
 
@@ -1076,6 +1077,7 @@ async def build_autoinject_hint(
             if i not in already and i != lesson_slot_id
         ],
         source="auto_inject",
+        project_id=project_id,
     )
 
     return {"context": "\n".join(lines), "note_ids": note_ids, "config": cfg}
@@ -2178,7 +2180,9 @@ async def build_write_path_hint(
                else "write_path_semantic")
         by_arm.setdefault(arm, []).append(int(item["id"]))
     for arm, ids in by_arm.items():
-        record_surfaced(user_id=user_id, note_ids=ids, source=arm)
+        record_surfaced(
+            user_id=user_id, note_ids=ids, source=arm, project_id=project_id,
+        )
 
     # ── Standing rules that may apply here (milestone 307) ──────────────
     #