Preserve connection capsules during IME composition

[tktm8]

Summary

• keep provisional IME text rendered without running connection-capsule overlap bookkeeping
• apply the committed edit once at composition end against the pre-composition value
• prevent composer commands and submission while the key event is part of active composition

Root cause

Mobile Safari can emit controlled-textarea changes during IME composition with a stale selection range. Processing each provisional value as a normal edit can make the edit appear to overlap a structured Connection capsule, removing it from the composer.

User impact

Japanese and other IME users can confirm text conversion in iOS Safari without losing an attached Connection capsule.

Validation

• pnpm --filter @gadgets/workshop-frontend build

Closes #92.
Related to #81.

[github-actions]

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[tktm8]

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[tktm8]

recheck

[tktm8]

Superseded by #94 after renaming the fork branch to fix/ios-ime-connection-capsules.