feat(app): add copy session ID actions

[anduimagui]

Issue for this PR

Closes #11937

Type of change

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

What does this PR do?

Adds copy-session-ID support in the app session view:

• adds a "Copy session ID" action in the session header copy/open controls
• adds a command palette/slash command (/id) to copy the active session ID
• adds the required English i18n keys and a specific error toast string

This complements #11938, which adds similar behavior in TUI command handling.

How did you verify your code works?

• Ran bun run --cwd packages/app typecheck successfully

Screenshots / recordings

Not included for this small UI/menu text action change.

Checklist

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

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Related PR found:

• feat: add /session-id command to copy session ID to clipboard #11938 - feat: add /session-id command to copy session ID to clipboard
  • This PR is complementary (as noted in the current PR's description). PR feat(app): add copy session ID actions #16376 adds copy-session-ID support in the app UI, while feat: add /session-id command to copy session ID to clipboard #11938 adds similar behavior in TUI command handling.
  • Both are addressing the same feature from different interfaces.

No other duplicate PRs found addressing the same feature.