fix(scheduler): treat /api/email/unread-state as passive UI poll

[michaelxer]

Summary

With the web UI open, scheduled/background agent runs were being aborted within about a minute and logged as Stopped by user, even though no real user interaction happened. The idle poll GET /api/email/unread-state was treated as foreground activity by _InteractiveActivityMiddleware, which calls stop_background_tasks_for_foreground(). Its sibling GET /api/email/urgency-state was already on the passive exact-path list; unread-state was missing.

This PR adds /api/email/unread-state to _PASSIVE_EXACT_PATHS in src/interactive_gate.py so the UI timer poll no longer pre-empts background work, and adds focused regression tests for the passive/interactive path classification.

Target branch

• This PR targets dev, not main.

Linked Issue

Fixes #5981

Type of Change

• Bug fix (non-breaking — fixes a confirmed issue)
• New feature (non-breaking — adds new behaviour)
• Breaking change (changes or removes existing behaviour)
• Refactor / cleanup (behaviour unchanged)
• Documentation only
• CI / tooling / configuration

What changed

1. src/interactive_gate.py: add /api/email/unread-state next to /api/email/urgency-state in _PASSIVE_EXACT_PATHS.
2. tests/test_interactive_gate_passive_paths.py: assert unread-state and urgency-state are passive; real interactive paths still track; OPTIONS still untracked.

No change to the foreground-gate design itself — only the passive allowlist for idle email polls.

How to Test

python -m pytest tests/test_interactive_gate_passive_paths.py -q
# 3 passed
python -m py_compile src/interactive_gate.py tests/test_interactive_gate_passive_paths.py

Manual (with web UI open):

1. Create a scheduled agent task that runs longer than ~60s.
2. Leave the Odysseus UI open so it polls /api/email/unread-state.
3. Force-run the task.
4. Expect the run to complete (or fail for real reasons), not abort as Stopped by user from foreground request GET /api/email/unread-state.

Checklist

• I searched open issues and open PRs — no open PR already fixes Scheduled/background agent runs are cancelled by the UI's own idle poll (/api/email/unread-state), logged as "Stopped by user" #5981 / unread-state passive path.
• This PR targets dev.
• Changes are limited to the passive path list + focused tests (no unrelated refactors).
• Full app e2e with a long scheduled agent run was not run on this Linux host. Path classification is covered by unit tests; the issue reporter already verified the one-line allowlist change locally against should_track_interactive_request() and a live scheduled run.

Visual / UI changes

None — backend gate classification only.

Limitations / notes

• Secondary suggestion from the issue (clearer abort message than Stopped by user) is intentionally out of scope here so the PR stays one-line + tests.