feat(web): align session action menus

[techotaku39]

Summary

Align the session-list context menu with the active session header by making Export conversation available from both entry points.

The lifecycle-specific actions remain intentionally different:

Session state	Available actions after #1060
Running	Rename, Export conversation, Copy resume command, Archive
Closed	Rename, Export conversation, Copy resume command, Reopen, Delete

Motivation

The session header already allows exporting both running and closed conversations, while the session-list context menu omits the export action. Users therefore have to open a conversation before they can export it, and the two menus expose different actions for the same session state.

Changes

• Add Export conversation to the session-list context menu for both running and closed sessions.
• Open the existing export format dialog directly from a session row.
• Change SessionExportDialog to accept a sessionId instead of a full Session object.
  • The export flow only needs the ID.
  • Session-list summaries can use the dialog without fetching the full session first.
• Keep lifecycle actions state-specific:
  • running sessions retain Archive
  • closed sessions retain Reopen and Delete
• Add coverage for opening the export dialog from both running and closed session rows.

This PR is intentionally separate from #1060. It only closes the pre-existing export-action gap between the two menus; #1060 adds Copy resume command to both surfaces independently.

Testing

• bun typecheck
• bun run typecheck:web
• bun run test:web
• bun run --cwd web test src/components/SessionList.directory-action.test.tsx src/components/SessionActionMenu.test.tsx
• git diff --check

bun run test was also attempted on Windows. The CLI suite exhausted the Bun process heap in codexRemoteLauncher.test.ts while the runner integration suite was still executing; the web suite and all checks relevant to this web-only change pass.

AI disclosure

Implementation and tests were produced with OpenAI Codex (GPT-5.6).

[github-actions]

Findings
None.

Summary
Review mode: initial
No issues found in the added/modified lines. Residual risk: static review only because local automation could not start in this runner.

Testing
Not run (automation: bun not found when attempting bun run --cwd web test src/components/SessionList.directory-action.test.tsx src/components/SessionActionMenu.test.tsx and bun run typecheck:web).

HAPI Bot