docs: update CLAUDE.md to reflect Oban worker architecture

Changes:
- Replace Exq references with Oban in LiveDashboard metrics section
- Add new 'Background Job Architecture' section documenting Oban workers
- Document DevicePollerWorker, DeviceMonitorWorker, DiscoveryWorker
- Update SNMP Polling Architecture to reference new workers
- Document automatic job lifecycle management
- Clarify direct Oban worker pattern (no GenServer/coordinator layer)

This ensures documentation matches the refactored architecture.

CLAUDE.md

@@ -172,10 +172,10 @@ LiveDashboard is available at `/dashboard` (requires authentication in productio
 - **Phoenix Metrics**: Request duration, route timings, channel/socket metrics
 - **Database Metrics**: Query time, decode time, queue time, idle time
 - **VM Metrics**: Memory usage, run queue lengths
-- **Exq/Background Jobs**:
-  - Queue sizes (default, discovery, polling, monitoring, maintenance)
-  - Busy worker processes
-  - Total worker processes
+- **Oban/Background Jobs**:
+  - Queue sizes (default, discovery, pollers, monitors, maintenance)
+  - Currently executing jobs
+  - Available jobs waiting to be processed
 - **Redis/Valkey**:
   - Connected clients
   - Memory usage (MB)
@@ -186,7 +186,7 @@ Metrics are collected every 10 seconds via `telemetry_poller` and published usin
 To view metrics:
 1. Navigate to `/dashboard` (or `/dev/dashboard` in development)
 2. Click the "Metrics" tab
-3. Scroll to see Exq and Redis sections
+3. Scroll to see Oban and Redis sections
 
 ## Project-Specific Constraints
 
@@ -277,21 +277,62 @@ curl https://towerops.net/api/v1/sites \
 - Sites: GET /api/v1/sites, POST /api/v1/sites, GET /api/v1/sites/:id, PATCH /api/v1/sites/:id, DELETE /api/v1/sites/:id
 - Devices: GET /api/v1/devices, POST /api/v1/devices, GET /api/v1/devices/:id, PATCH /api/v1/devices/:id, DELETE /api/v1/devices/:id
 
+### Background Job Architecture (Oban)
+
+The application uses **Oban** (PostgreSQL-backed job queue) for all background processing. Jobs are distributed across the cluster and automatically retried on failure.
+
+**Oban Queues:**
+- `default` (10 workers) - General background tasks
+- `discovery` (10 workers) - SNMP discovery jobs
+- `pollers` (50 workers) - SNMP polling (one job per device)
+- `monitors` (50 workers) - Device health monitoring (one job per device)
+- `maintenance` (5 workers) - Cleanup and housekeeping tasks
+
+**Key Oban Workers:**
+
+1. **`DevicePollerWorker`** - SNMP polling for time-series data
+   - Runs every 60 seconds per device (configurable via `check_interval_seconds`)
+   - Collects: sensor readings, interface stats, neighbor topology, ARP/MAC tables
+   - Uses Oban `unique` constraint to prevent duplicate jobs
+   - Self-schedules next poll after completion
+   - Broadcasts PubSub events for real-time UI updates
+
+2. **`DeviceMonitorWorker`** - Health monitoring via ping
+   - Runs every 30 seconds per device
+   - Performs ICMP ping checks to detect device up/down status
+   - Creates alerts on status changes
+   - Self-schedules next check after completion
+
+3. **`DiscoveryWorker`** - One-time SNMP discovery
+   - Triggered manually or on device creation
+   - Collects: system info, interfaces, sensors, neighbors
+   - Creates/updates SNMPDevice record with full topology
+
+4. **`NeighborCleanupWorker`** - Maintenance task
+   - Runs periodically to clean up stale neighbor data
+   - Deletes neighbors older than 24 hours
+
+**Automatic Job Management:**
+- Jobs are automatically started when `monitoring_enabled` or `snmp_enabled` is set to `true`
+- Jobs are automatically stopped when disabled or device is deleted
+- All job lifecycle managed in `Devices` context (create_device, update_device, delete_device)
+
 ### SNMP Polling Architecture
 
 The application has two separate SNMP collection mechanisms:
 
 **1. Discovery (`Towerops.Snmp.Discovery`)** - One-time or manual collection
-- Triggered manually by user or on a schedule
+- Triggered manually by user or via `DiscoveryWorker` Oban job
 - Collects: system info, device identification, interfaces, sensors, **neighbors**
 - Creates/updates the device record and all associated data
 - Typically runs when equipment is first added or when user clicks "Rediscover"
 
-**2. Polling (`Towerops.Snmp.PollerWorker`)** - Continuous time-series collection
+**2. Polling (`DevicePollerWorker`)** - Continuous time-series collection
 - Runs automatically every 60 seconds (configurable per equipment)
 - Collects: sensor readings, interface statistics, **neighbor topology**
 - Updates time-series data without recreating device records
 - Keeps neighbor data fresh by polling LLDP/CDP every minute
+- **Architecture**: Direct Oban worker (no GenServer or coordinator layer)
 
 **Neighbor Data Lifecycle:**
 - Discovery saves initial neighbors with 5-minute stale threshold