PHPSTAN: validate against version 3,4 & 5

[masteradhoc]

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What?

Raise PHPStan baseline in this branch from level 4 to level 5 and fix all resulting level 5 findings so the full repository passes static analysis and lint checks.

Why?

The plugin already passed at level 2, but level 3,4 & 5 surfaced stricter type-safety issues (mostly scalar typing around escaping and auth-code handling). Fixing these now improves type correctness, keeps CI healthier as rules tighten, and reduces future refactor risk.

How?

This PR updates the PHPStan level and applies targeted, behavior-preserving type fixes

Use of AI Tools

AI assistance: Yes
Tool(s): GitHub Copilot
Model(s): GPT-5.3-Codex
Used for: Static analysis triage, proposing and applying type-safety fixes, and drafting PR documentation.
Human review: All generated changes were reviewed and validated through local lint/static-analysis runs.

Testing Instructions

1. Install dependencies:
   npm install

2. Run full lint suite:
   npm run lint

3. Run PHPStan directly with repo config:
   vendor/bin/phpstan analyse -c phpstan.dist.neon --memory-limit=1G

4. Optional explicit level check:
   vendor/bin/phpstan analyse -c phpstan.dist.neon --level=5 --memory-limit=1G

Expected result:

• All commands complete successfully.
• PHPStan reports OK with no errors.

Screenshots or screencast

Not applicable (no UI behavior change).

Before	After
PHPStan level 5 reported 14 errors across core/providers/settings	PHPStan level 5 reports no errors

Changelog Entry

Development Update - Raise PHPStan to level 5 and resolve level 5 type-safety findings across core and providers.

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