Correct INTENT 5.1 to the maintainer's words; decide remember_saveable, getValue/setValue and the coroutine scopes #100

The maintainer corrected the record (2026-10-04, relayed by the ecosystem lead). On 2026-10-03 the instruction was only: a more declarative API than main.App.update(), with no explicit update function. 544641c also did three things the maintainer never instructed:

1. moved the state inside App to module level (main.messages);
2. made remember_saveable 'not provided';
3. treated getValue()/setValue() as an implementation constraint.

INTENT §5.1 recorded all three as decisions.

Decided now:

• remember_saveable is supported with rememberSaveable's meaning (it survives rotation and process restart), int/long/bool/float/str first, as in pycomposeui.
• Notebook cells 9-13 work as written. The app attaches the state to its root (App.messages = messages = remember_saveable(""), as the 2024 demo PyREPL abc6952 did), and the notebook reads and writes it with getValue()/setValue(...). .value is a Pythonic alias.
• The Kotlin side is a @Composable rememberSaveableWrapper in python-multiplatform-compose (the lead's PMP issue).
• DefaultCoroutineScope and MainCoroutineScope are built on pythonx-concurrent, and implemented after it.
• state() is untouched while the maintainer decides whether to keep it.

This issue covers the documents: INTENT §4 and §5, SPEC S5.4 and §8 plus a new S5.6 and S5.7, PROJECT, README en/ko and the guide. The implementation follows in its own issue. Done when the docs say this and counts are unchanged.