fix(lint): review and enable rules from @nextcloud/eslint-config v9 migration

[masterlouis]

Follow-up of #7876. Reviews and progressively enables the ESLint rules
newly introduced by @nextcloud/eslint-config v9, as tracked in
libresign/disabled-during-migration in eslint.config.mjs.

Work in progress — see commits for individual rules enabled so far.

Done so far

• Fixed config scoping bugs surfaced by the v9 upgrade:
  • vue/no-unused-components needs files: ['**/*.vue'] since the
    vue plugin is only registered for .vue files in v9.
  • import/order and import/no-unresolved referenced
    eslint-plugin-import, which was removed entirely in v9 (replaced
    by perfectionist/sort-imports and import-extensions/*).
• Removed obsolete eslint-disable comments referencing rules that no
  longer exist or no longer apply in their file's context.
• Added libresign/disabled-during-migration block listing all rules
  pending review, as the source of truth for this task.

Still to do

• Enable remaining rules one by one, one commit per rule.