feat(scheduler): Immutable schedules and HTTP-only pipeline

## Changes
- **Migration 089**: Add is_immutable and method columns to task_schedules
  - Per-state product_discovery schedules (4h default)
  - Store discovery weekly (168h)
  - All schedules use HTTP transport (Puppeteer/browser)
- **Task Scheduler**: HTTP-only product discovery with per-state scheduling
  - Each state has its own immutable schedule
  - Schedules can be edited (interval/priority) but not deleted
- **TasksDashboard UI**: Full immutability support
  - Lock icon for immutable schedules
  - State and Method columns in schedules table
  - Disabled delete for immutable, restricted edit fields
- **Store Discovery HTTP**: Auto-queue product_discovery for new stores
- **Migration 088**: Discovery payloads storage schema

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/migrations/088_discovery_payloads.sql

@@ -0,0 +1,30 @@
+-- Migration 088: Extend raw_crawl_payloads for discovery payloads
+--
+-- Enables saving raw store data from Dutchie discovery crawls.
+-- Store discovery returns raw dispensary objects - save them for historical analysis.
+
+-- Add payload_type to distinguish product crawls from discovery crawls
+ALTER TABLE raw_crawl_payloads
+ADD COLUMN IF NOT EXISTS payload_type VARCHAR(32) NOT NULL DEFAULT 'product';
+
+-- Add state_code for discovery payloads (null for product payloads)
+ALTER TABLE raw_crawl_payloads
+ADD COLUMN IF NOT EXISTS state_code VARCHAR(10);
+
+-- Add store_count for discovery payloads (alternative to product_count)
+ALTER TABLE raw_crawl_payloads
+ADD COLUMN IF NOT EXISTS store_count INTEGER;
+
+-- Make dispensary_id nullable for discovery payloads
+ALTER TABLE raw_crawl_payloads
+ALTER COLUMN dispensary_id DROP NOT NULL;
+
+-- Add index for discovery payload queries
+CREATE INDEX IF NOT EXISTS idx_raw_crawl_payloads_type_state
+  ON raw_crawl_payloads(payload_type, state_code)
+  WHERE payload_type = 'store_discovery';
+
+-- Comments
+COMMENT ON COLUMN raw_crawl_payloads.payload_type IS 'Type: product (default), store_discovery';
+COMMENT ON COLUMN raw_crawl_payloads.state_code IS 'State code for discovery payloads (e.g., AZ, MI)';
+COMMENT ON COLUMN raw_crawl_payloads.store_count IS 'Number of stores in discovery payload';