feat(token-tracking): introduce token note taxonomy (measured/userbased/workplan/heuristic)

Tier 1 (exact counts) now defaults to note="measured" instead of null,
signalling the counts were read from the Claude Code status bar.
Callers can pass note="userbased" when a human provided the numbers.

  measured  — agent read exact counts from the Claude Code status bar
  userbased — counts provided by a human
  workplan  — prorated from workplan total across task count
  heuristic — server fallback, 1000/500, no agent input

Added token_note field to TaskUpdate schema and exposed note param on
update_task_status and record_interactive_task MCP tools.
TOOLS.md documents the full taxonomy. 185 tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_token_passthrough.py

@@ -65,7 +65,25 @@ class TestTokenPassthrough:
         assert ev["model"] == "claude-sonnet-4-6"
         assert ev["agent"] == "custodian"
         assert ev["workstream_id"] == ws["id"]
-        assert ev["note"] is None
+        assert ev["note"] == "measured"
+
+    async def test_tier1_userbased_note_override(self, client):
+        """Tier 1 with note='userbased' records that note instead of 'measured'."""
+        await _create_domain(client)
+        topic = await _create_topic(client)
+        ws = await _create_workstream(client, topic["id"])
+        task = await _create_task(client, ws["id"])
+
+        r = await client.patch(f"/tasks/{task['id']}", json={
+            "status": "done",
+            "tokens_in": 500,
+            "tokens_out": 200,
+            "token_note": "userbased",
+        })
+        assert r.status_code == 200
+
+        events = (await client.get("/token-events/", params={"task_id": task["id"]})).json()
+        assert events[0]["note"] == "userbased"
 
     async def test_tier2_workplan_prorated(self, client):
         """Tier 2: workplan totals prorated across 4 tasks → 250/125 each, note='workplan'."""