feat(brain): audit-log every tools/call; server-owned write provenance (#147)

Closes #144 (audit line per tools/call) and #145 (origin/written_by stamped on every model-reachable write, surfaced in brain_query/brain_get).

Passed pr-gatekeeper after four rounds of adversarial review, verified by execution: #147

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Mathias <mthbqv@gmail.com>

ingestion/internal/mcp/tools_notes_test.go

@@ -66,8 +66,11 @@ func TestBrainReadAndEdit_RoundTripThroughJSONRPC(t *testing.T) {
 
 	got, err := os.ReadFile(filepath.Join(dir, "wiki/homelab/facts/n.md"))
 	require.NoError(t, err)
-	assert.Equal(t, "---\ntitle: 'n'\n---\n\nalpha\nBETA\n", string(got),
-		"only the matched bytes may change")
+	// Only the matched bytes change in the body; the one deliberate addition
+	// is the editor's provenance stamp (hyperguild#145 — no principal here,
+	// so origin: unknown).
+	assert.Equal(t, "---\ntitle: 'n'\norigin: unknown\n---\n\nalpha\nBETA\n", string(got),
+		"only the matched bytes and the provenance stamp may change")
 }
 
 func TestBrainEdit_EmptyOldStrErrorNamesRawArgumentBytes(t *testing.T) {