Invoke Scenario Prompt Scheduler Service with per-activity error isolation

Implement the per-activity loop as a standard `for...of` loop (not `Promise.all`) so errors are isolated sequentially. Use a `RunSummary` typed object initialised before the loop: `{ total: 0, succeeded: [], skipped: [], errors: [], startedAt: Date.now() }`. Increment `total` at the top of each iteration. In the catch block, push `{ activity_id, reason: err.message }` to `errors` — truncate `err.message` to 200 characters before logging to avoid log bloat.

Distinguish between 'business skip' (idempotency, inactive status — handled in task-005) and 'processing error' (unexpected exception) by checking for a sentinel `SkipSignal` thrown by the Scheduler Service. Avoid swallowing errors silently: always push to the appropriate array. After the loop, compute `duration_ms = Date.now() - startedAt` and emit the final log entry before returning the HTTP response.

Unit tests (Deno test runner): (1) mock Scheduler Service returns success for all activities → summary shows all succeeded; (2) mock Scheduler Service throws for activity index 2 of 5 → activities 1, 3, 4, 5 still processed, error array contains index 2; (3) mock Scheduler Service is unavailable → function aborts early with structured error log. Integration test: deploy to Supabase staging, inject 3 test activity records, verify summary object in logs matches expected counts. No Flutter-side tests needed for this task — it is a pure backend Edge Function concern.