Tasks: Migrate UI pause/resume to dedicated Tasks endpoints #1330

Repo: coder/coder

Scope: Update the task pause/resume UI implementation to use the dedicated Tasks Pause/Resume API endpoints instead of Workspace stop/start operations.

Background:
The initial implementation (#1267) uses workspace stop/start operations under the hood for pausing/resuming tasks. Once the dedicated Tasks Pause/Resume endpoints are available, we should migrate to use these directly for cleaner semantics and potential future task-specific behaviors.

Changes:

• Replace workspace stop API calls with Tasks Pause endpoint
• Replace workspace start API calls with Tasks Resume endpoint
• Update React Query mutations to use new endpoint paths
• Update polling/status checks to use task-centric status if available
• Remove workspace-specific build waiting logic in favor of task status polling (if applicable)