fix: queue concurrent subagent questions

[lucas-gaitzsch]

Issue for this PR

Closes #36915

Type of change

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

What does this PR do?

Collects pending questions across the full root session tree, orders them by request ID, and keeps the active request selected until it resolves.

The TUI now remounts prompt state per request, preserves interrupted drafts, blocks duplicate submissions, and routes replies through the owning session location. Desktop/web uses the same sticky queue selection and owner-location routing.

How did you verify your code works?

• Added queue tests for sibling and nested subagents, FIFO ordering, sticky selection, and tree isolation.
• packages/tui: 194 passed, 1 skipped; typecheck passed.
• packages/app: targeted queue tests and typecheck passed.
• The full app unit suite has 612 passing tests and one unrelated existing i18n parity failure for three missing Arabic keys.

Screenshots / recordings

Not applicable; this changes request selection and routing without changing the UI.

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:

Based on my search, I found one potentially related PR that might be worth reviewing in context:

Related PR:

• fix(tui): preserve prompts during session hydration #36433 - fix(tui): preserve pending session work — This PR is related to preserving TUI state and pending work, which aligns with the current PR's goal of preserving interrupted drafts and maintaining queue state across the TUI.

However, this appears to be addressing a different but complementary aspect (preserving session work) rather than a duplicate of the current PR's focus on queueing and routing concurrent subagent questions.

The current PR (#36916) is the primary PR implementing the queue management for concurrent subagent questions and does not appear to have exact duplicates in the open PR list.