Fix Gemini Send All behavior in localized interfaces

[Manho]

Summary

• Target Gemini's localized send button and keep a locale-independent icon fallback.
• Remove the broad Gemini button selector that could match Upload & tools.
• Add Gemini content-script coverage for localized sending, auto-submit, missing or disabled send buttons, and image injection.

Root cause

The fallback selector .input-area-container button:has(mat-icon) matched any icon button inside Gemini's composer. When the English send-button selectors did not match the Chinese interface, Panelize could click Upload & tools instead of sending the prompt.

User impact

Send All now targets Gemini's actual send control in localized interfaces and no longer opens the upload menu as a fallback. The image-upload path is unchanged and covered by a regression test.

Fixes #53

Validation

• npx vitest run --exclude='tests/e2e/**' --reporter=dot --silent (36 files, 304 tests passed)
• npx vitest run tests/gemini-content-script.test.js --reporter=dot --silent (7 tests passed)
• Computer Use verification with the current repository loaded as an unpacked extension: confirmed the Chinese Gemini send control is labeled 发送, and Send All no longer opens Upload & tools when no send control is available.