feat: Add Real-Time Inventory Tracking infrastructure

Implements per-store high-frequency crawl scheduling and inventory
snapshot tracking for sales velocity estimation (Hoodie Analytics parity).

Database migrations:
- 117: Per-store crawl_interval_minutes and next_crawl_at columns
- 118: inventory_snapshots table (30-day retention)
- 119: product_visibility_events table for OOS/brand alerts (90-day)

Backend changes:
- inventory-snapshots.ts: Shared utility normalizing Dutchie/Jane/Treez
- visibility-events.ts: Detects OOS, price changes, brand drops
- task-scheduler.ts: checkHighFrequencyStores() runs every 60s
- Handler updates: 2-line additions to save snapshots/events

API endpoints:
- GET /api/tasks/schedules/high-frequency
- PUT /api/tasks/schedules/high-frequency/:id
- DELETE /api/tasks/schedules/high-frequency/:id

Frontend:
- TasksDashboard: Per-Store Schedules section with stats

Features:
- Per-store intervals (15/30/60 min configurable)
- Jitter (0-20%) to avoid detection patterns
- Cross-platform support (Dutchie, Jane, Treez)
- No crawler core changes - scheduling/post-crawl only

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

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

backend/Dockerfile

@@ -12,7 +12,13 @@ RUN apt-get update && apt-get install -y \
 WORKDIR /app
 
 COPY package*.json ./
-RUN npm install
+
+# Install dependencies with retry and fallback registry
+RUN npm config set fetch-retries 3 && \
+    npm config set fetch-retry-mintimeout 20000 && \
+    npm config set fetch-retry-maxtimeout 120000 && \
+    npm install || \
+    (npm config set registry https://registry.npmmirror.com && npm install)
 
 COPY . .
 RUN npm run build