Lint debt cleanup post-canonical-sync (Phase 2 fleet rollout)

[rubenvdlinde]

Context

Tracking issue for lint debt remaining after the Phase 2 fleet-wide canonical
root-config sync. Sibling PRs landed on shillinq (#300), decidesk (#243), and
this PR on deskdesk.

The canonical configs (phpcs.xml, phpmd.xml, psalm.xml, phpstan.neon,
custom sniffs) now match nextcloud-app-template exactly. No per-app rule
weakening — anything that couldn't be fixed mechanically is captured here.

phpstan baselined errors (1)

• lib/Service/SettingsService.php:244 — \OC::$SERVERROOT legacy server
  accessor. Replace with a proper path-resolution alternative
  (IServerContainer / IConfig paths, or pass the NC root in via DI).
  The current usage resolves the bundled register JSON file relative to
  /var/www/html to satisfy ConfigurationService::importFromFilePath.

phpmd architectural violations (1)

• BooleanArgumentFlag —
  lib/Service/SettingsService.php:228 SettingsService::loadConfiguration
  takes a bool $force flag (Single Responsibility violation). Public
  method, requires API redesign — split into loadConfiguration() and
  forceLoadConfiguration() or accept an enum/options object.

phpcs warnings (21, informational only)

phpcs reports 0 errors, 21 warnings across 12 files (mostly Generic.Files.LineLength
and complexity hints). Tracked here for future complexity refactors but not
blocking — phpcs gate passes.

Out of scope here

Per the Phase 2 directive, this PR does not weaken any per-app validation
rules — those decisions stay fleet-wide in the canonical templates.