feat(meta): expose effective experimental flag state and show it in Lab

GET /meta flattened flags to booleans, so the web Lab tab could not tell
a saved setting from an environment override: the switch showed the
config value while the runtime used something else.

- FlagService.explain() now carries externallyControlled (source is env
  or master-env) and overridden (a saved value exists and differs from
  the effective value); both decided in core, never inferred by a UI.
- GET /meta adds experimental_flag_states beside the boolean map.
- The web client maps them, keeps them in workspace state, exposes
  experimentalFlagState(id), and the Lab rows show "Environment
  controlled" and "Saved setting overridden" chips independently.
- klient flags contract mirrors the two new fields.

Author: elkaix

.changeset/lab-flag-effective-state.md

@@ -0,0 +1,5 @@
+---
+"@pymodel/pythinker-code": minor
+---
+
+The Lab settings show when an experimental flag is controlled by the environment and when the saved setting is overridden.

apps/pythinker-code/dist-web/.web-bundle-manifest.json

@@ -1,4 +1,4 @@
 {
-  "sourceHash": "de035986f5cd2b25cb86fe5a4fccb3b7cace86f47da191388a3b2485f2fc0093",
+  "sourceHash": "fd8373670e82925e4ab4b518d59498b2f1c18bfe495af7e88c946db7ce1e9b65",
   "sourceFileCount": 405
 }