🔒 GDPR tasks data provider (tasks.init.js)

[PierreBrisorgueil]

Self-register the tasks module's GDPR provider.

Scope — modules/tasks/tasks.init.js

• Add registerDataProvider({ key:'tasks', axis:'user', retention:'delete', export, erase }) alongside the existing onOrganizationRemoved.
• Reuse TasksDataService.list / remove (no new query logic).

DoD

• Init unit test: registers exactly once, delegates user-scoped, import-alone-doesn't-register, module-deactivated → provider absent (no crash).
• /verify green.

Depends on: GDPR registry leaf.

Created via /dev:issue