fix(api,watcher,server): reject moves non-markdown untouched; read caps; BOM; strict routing flag (review of #211, pass 2)

- brain_reject on a parked pdf/txt moves the bytes; it no longer prepends YAML
- raw/ notes are read through a cap (readCapped); an endless reader test fails
  instead of exhausting memory
- a byte-order mark no longer hides a note's wing: key
- INGEST_WING_ROUTING is parsed strictly; a typo stops the server rather than
  leaving routing silently off
- tests for the reserved-wing check in every disguise (Sources, sources., ...)
Mutation-checked.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/cmd/server/main_test.go

@@ -100,3 +100,32 @@ func TestClaudeSinkDoesNotWriteThroughASymlinkedArchiveDir(t *testing.T) {
 		})
 	}
 }
+
+func TestEnvFlag(t *testing.T) {
+	tests := []struct {
+		name, set string
+		want      bool
+		wantErr   bool
+	}{
+		{"unset is off", "", false, false},
+		{"1", "1", true, false},
+		{"true", "true", true, false},
+		{"TRUE", "TRUE", true, false},
+		{"0", "0", false, false},
+		{"false", "false", false, false},
+		{"a typo is an error, not silently off", "ture", false, true},
+		{"yes is not a bool here", "yes", false, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("TEST_ENV_FLAG", tt.set)
+			got, err := envFlag("TEST_ENV_FLAG")
+			if tt.wantErr {
+				assert.Error(t, err)
+				return
+			}
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}