Refine feature identity and state actions

[tiye]

Summary

• install opaque ambient feature identity at feature_root(...), with feature_key() and feature_marker(name) for descendants
• remove panel_key forwarding from Todo/Lab helpers and keep multi-instance store, listener, effect, and DOM marker isolation
• make Todo save and Lab reply domain actions carry their current component values as versioned serializable payloads
• keep component-store transitions local to the originating event instead of letting domain reducers/workflows read or write child stores
• remove the unused public cross-component store read/write/clear API and feature-specific path coordination helpers
• update README, developer guidance, plan, tests, and GitHub tracking

Verification

• yarn test:koka — 64/64 pass
• yarn check — Koka compile and Vite production bundle pass
• browser smoke: Todo edit/save with escaped payload characters
• browser smoke: Lab reply sends the typed message and clears its component draft
• browser smoke: component draft survives Koka HMR regeneration and a full reload through localStorage
• browser console: no errors

Closes #7.

Follow-ups are tracked separately in #8 (action replay) and #9 (framework lifecycle cleanup for unreachable keyed child stores).

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