fix(app): recover prompt text from editor dom; route v1 follow-ups to their session directory

[CannonRS]

Issue for this PR

Closes #48528
Closes #48529

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Two small fixes in the app's prompt submission path.

Recover text when the store is empty but the DOM editor still holds it (Closes #48528). createPromptSubmit parsed the prompt from the store-backed state only. When that state is empty but the DOM editor element still contains text (e.g. after a navigation or state reset), the submit saw an empty prompt and returned early, silently discarding the typed message. The fix falls back to parsing the DOM editor element via a new parsePromptInputV2Editor helper when the store is empty and no images or comments are present, and sends the recovered text.

Send v1 follow-up prompts to their session directory (Closes #48529). The V1 compat API's prompt path always used the directory the client was created with (the project directory), ignoring the session's own directory. The app now passes sessionDirectory when sending a follow-up draft, and the compat layer routes the prompt to that directory instead.

How did you verify your code works?

• bun typecheck (tsgo) passes in packages/app and packages/session-ui.
• submit.test.ts passes 9/9, including a new regression test that submits recovered text from a DOM editor element when the store is empty.
• git diff --check clean; no unrelated changes.

Screenshots / recordings

n/a (non-UI behaviour; recovery happens before the prompt is sent)

Fork

• Source fork: https://github.com/mQorva/OpenCode
• Diff against this fork's dev: mQorva/OpenCode@dev...prompt-submit-fixes
• mQorva issue / context: n/a

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR