fix(claudewatcher): tag session-dump notes source_type: internal

brain-gardener#5: the audit's unsourced check was flagging 59 raw
claudewatcher session dumps as high-severity hallucination risk,
because it can't distinguish a first-party observation (a session
transcript) from an external claim needing citation.

Adds WriteNoteOptions.SourceType, emitted as source_type: <value> in
the wing/hall frontmatter route. claudeSink (the claudewatcher sink)
now always sets source_type: internal on the notes it writes.

ingestion/internal/api/handler_test.go

@@ -118,6 +118,40 @@ func TestWrite_IncludesFrontmatterWhenTypeProvided(t *testing.T) {
 	assert.Contains(t, string(content), "Some learning.")
 }
 
+func TestWriteNote_HallRouteIncludesSourceTypeWhenSet(t *testing.T) {
+	dir := t.TempDir()
+
+	rel, err := api.WriteNote(dir, api.WriteNoteOptions{
+		Content:    "# Claude session abc (koala)\n\nBody.\n",
+		Filename:   "session-koala-abc",
+		Wing:       "claude-sessions",
+		Hall:       "facts",
+		Type:       "source",
+		SourceType: "internal",
+	})
+	require.NoError(t, err)
+
+	got, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(rel)))
+	require.NoError(t, err)
+	assert.Contains(t, string(got), "source_type: internal")
+	assert.Contains(t, string(got), "wing: claude-sessions")
+}
+
+func TestWriteNote_HallRouteOmitsSourceTypeWhenUnset(t *testing.T) {
+	dir := t.TempDir()
+
+	rel, err := api.WriteNote(dir, api.WriteNoteOptions{
+		Content: "manually captured fact.\n",
+		Wing:    "agentsquad",
+		Hall:    "facts",
+	})
+	require.NoError(t, err)
+
+	got, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(rel)))
+	require.NoError(t, err)
+	assert.NotContains(t, string(got), "source_type")
+}
+
 func TestWrite_GeneratesFilenameIfAbsent(t *testing.T) {
 	dir, h := setup(t)
 	body, _ := json.Marshal(map[string]any{"content": "auto name"})