Fix composer send button contrast

[erickkkyt]

What changed

• include the semantic data-awesome-codex-composer-control="primary" marker in the shared send-button adapter selector
• preserve contrasting theme foreground/background colors on current Codex composer markup
• cover the current 26.715.31925 markup with a regression test

Verification

• 34 test files / 267 tests passed
• 12 theme packages validated
• TypeScript and production build passed
• production dependency audit found no known vulnerabilities
• live nocturne-lite verification: accent background and dark arrow are visibly distinct