fix(config): synchronize API updates with the global runtime config

[HC-ONLINE]

Description

Fixes configuration updates made through the API being applied only to a request-local ConfigLoader instead of the process-wide configuration used by the application.

ConfigService() now uses the global loader when no explicit config path is supplied. Updates, resets, and loads mutate the shared configuration object in place, preserving object identity for runtime consumers. Services constructed with an explicit config_path remain isolated for CLI and test use cases.

The change also validates candidate configuration values before applying them, documents runtime versus startup-only settings, and adds regression coverage for API-key revocation and global synchronization.

Related Issue

Fixes the confirmed configuration runtime synchronization bug.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• I have followed the style guidelines of this project (Ruff & Pyright)
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly

Validation

• uv run pytest -q — 1548 passed, 2 skipped
• uv run ruff check . — passed
• uv run ruff format . --check — passed
• uv run pyright — 0 errors
• uv run pre-commit run --all-files — code-quality hooks passed; the existing Prettier failure affects unrelated historical Markdown/YAML files and was reproduced from a clean HEAD.

Screenshots (if applicable)

Not applicable.