Reconcile policies again when the signed-in user changes

[Frooodle]

Description of Changes

• usePolicies reconciled only on mount, so a fetch that ran before there was a session left every category in its unconfigured default.
• That default is indistinguishable from "the backend has no policy", because policyStorage.defaultState() returns exactly the same shape.
• The local-pass engine reads it as "no policy" and stops running, so classification is silently dormant — on uploads, not just the Downloads offer.
• Reconcile now re-runs whenever the signed-in user changes, which repopulates the cache from the backend after login.
• Also re-runs on sign-out, so one user's policies do not linger for the next.

Why: reproduced on a real desktop install — the Policies page read the backend live and showed Classification enabled, while the app's own cache said unconfigured and nothing classified.

Scope: shared policy plumbing, so it affects web and SaaS as well as desktop. Independent of the other desktop PRs.

Known remaining: the cache still cannot express "unknown" versus "off". This removes the common cause rather than the conflation itself.

Ran: frontend:typecheck:all, frontend:lint, frontend:format:check, full vitest (3440), comment-lint.

---

Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• Every comment I added says something the code does not (guide)
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have run task check to verify linters, typechecks, and tests pass
• I have tested my changes locally. Refer to the Testing Guide for more details.

[github-actions]

🚀 V2 Auto-Deployment Complete!

🔗 Direct Test URL (non-SSL) http://54.175.155.236:7966

🧩 Admin portal included - try it at http://54.175.155.236:7966/portal.

This deployment will be automatically cleaned up when the PR is closed.

🔄 Auto-deployed for approved V2 contributors.