feat: add composer send/stop button aligned with the Qoder IDE

[luoxuanzao]

Summary

• Add a send/stop action button to the chat composer toolbar: send (arrow-up) when idle, stop (filled square) while streaming, mirroring the Qoder IDE composer affordance.
• IDE-aligned styling: brand-green rounded square with a soft dark (70% black) arrow; dimmed and non-clickable when the composer is empty; grouped flush against the permission toggle at the row's right edge (with a fallback that keeps right alignment when the toggle is hidden).
• Send routes through the input controller (and the existing Enter path in instruction/bang modes); stop calls cancelStreaming; availability tracks input text, attached images, and streaming-state changes.
• Localize composer.send / composer.stop across all 10 locales; add component tests and a CHANGELOG entry.
• Why: mouse-only users had no way to send or interrupt a run; the IDE already ships this control, so the plugin now matches it.

Verification

• npm run typecheck
• npm run lint
• npm run test (142 suites / 3306 tests green)
• npm run build
• npm run release:check
• npm run audit:prod (0 vulnerabilities)
• Tested affected qodercli behavior against a real CLI when applicable — verified in a real test vault against the live SDK: empty-disabled, enable-on-typing, send-on-click, stop icon during a real streaming run, click-to-interrupt, and recovery to disabled.

Safety

• No credentials, private vault content, internal URLs, or personal paths are included
• User-visible changes are documented in CHANGELOG.md