[Bug]: PPOM - Validations not working wiht Firefox Privacy Mode

Describe the bug

Recently @david.murdoch and @mark.stacey discovered that IndexedDB is not available in Firefox for private browsing mode.
This was causing an infinite loading spinner on the wallet side, and a workaround was added by David. Additionally a bug was open on Mozilla's end here.
This bug can also affect Blockaid validations when using PPOM with FF in private mode, as it also uses IndexedDB.

Thread: https://consensys.slack.com/archives/C03ETQA9EPK/p1755624859736669

Expected behavior

It seems that the solution here should be what Mark suggested:

I had suggested that we migrate PPOM storage to the controller, and persist state through the controller like with most other features.
The issue I was thinking of was completed here: https://github.com/MetaMask/ppom-validator/pull/56It seems that IndexedDB is no longer required as the storage backend as of that PR. But we never actually migrated away from it. We just removed one obstacle to migrating away from IndexedDB. (edited)

Steps to reproduce

1. Enable "Always use private browsing mode" (Settings -> Privacy and Security -> History -> Firefox will, then select Use custom settings for history -> then check Always use private browsing mode
2. Install MetaMask
3. Block Blockaid API requests
4. Trigger a tx
5. Validations should don't happen

Error messages or log output

Detection stage

In production (default)

Version

13.1.0

Build type

None

Browser

Firefox

Operating system

Linux

Review the PPOM storage and controller persistence paths, using ppom-validator PR #56 and the workaround in metamask-extension PR #35040 as context. Reproduce the failure in Firefox private browsing with Blockaid API requests blocked, then verify that PPOM validations complete without relying on IndexedDB.