Stop auto-populating create PR fields

[brennanb2025]

Summary

• Stop seeding Create PR title and description from commit subjects
• Keep the base branch default, but require explicit or generated reviewer-facing copy
• Improve the draft control to a full-width Create as draft checkbox row

Tests

• pnpm run typecheck
• pnpm run lint
• git diff --check origin/main...HEAD
• pnpm vitest run --config config/vitest.config.ts src/main/source-control/hosted-review-creation.test.ts
• pnpm test:e2e -- tests/e2e/source-control-create-pr.spec.ts
• Electron/CDP validation from /Users/thebr/orca/workspaces/orca/Create-PR-auto-populate; verified window.api.app.getIdentity() matched brennanb2025/Create-PR-auto-populate.
• Used demo-project for the live app workflow: verified the real eligibility path returns no auto-generated title/body, opened the Create PR composer with empty title/description and base main, filled title/body, toggled Create as draft, clicked Create draft PR, and captured the dry-run payload with draft: true and the demo-project worktree path.
• Inspected console/app logs for relevant failures; only warning was expected from the fake dry-run PR number not existing after the captured submit.

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