feat(tasks): add browser and terminal task tab launch options

[arnestrickmann]

Summary

• port the create-conversation modal to reuse the initial conversation composer on the current paneLayout tab system
• let modal callers open optional browser tabs through their owning pane layout
• add terminal as a first-class task tab backed by existing terminal/PTY infrastructure

Stacked Change Notes

• Commit 1 ports the PR feat(tasks): add prompt and browser options to conversation modal #2673 behavior to current main APIs.
• Commit 2 stacks terminal task tabs on top of that modal/browser flow.

Validation

• corepack pnpm exec vitest run --project node src/renderer/features/tasks/commands.test.ts src/renderer/features/tabs/pane-store.test.ts src/renderer/features/tasks/create-task-modal/build-create-task-params.test.ts
• corepack pnpm run typecheck
• corepack pnpm run lint
• corepack pnpm run format:check