Add distributed agent architecture for multi-node signal intelligence

Features:
- Standalone agent server (intercept_agent.py) for remote sensor nodes
- Controller API blueprint for agent management and data aggregation
- Push mechanism for agents to send data to controller
- Pull mechanism for controller to proxy requests to agents
- Multi-agent SSE stream for combined data view
- Agent management page at /controller/manage
- Agent selector dropdown in main UI
- GPS integration for location tagging
- API key authentication for secure agent communication
- Integration with Intercept's dependency checking system

New files:
- intercept_agent.py: Remote agent HTTP server
- intercept_agent.cfg: Agent configuration template
- routes/controller.py: Controller API endpoints
- utils/agent_client.py: HTTP client for agents
- utils/trilateration.py: Multi-agent position calculation
- static/js/core/agents.js: Frontend agent management
- templates/agents.html: Agent management page
- docs/DISTRIBUTED_AGENTS.md: System documentation

Modified:
- app.py: Register controller blueprint
- utils/database.py: Add agents and push_payloads tables
- templates/index.html: Add agent selector section

static/css/index.css

@@ -1840,6 +1840,27 @@ header h1 .tagline {
     letter-spacing: 1px;
 }
 
+/* Agent status indicator */
+.agent-status-dot {
+    width: 10px;
+    height: 10px;
+    border-radius: 50%;
+    flex-shrink: 0;
+}
+
+.agent-status-dot.online {
+    background: var(--accent-green);
+    box-shadow: 0 0 6px var(--accent-green);
+}
+
+.agent-status-dot.offline {
+    background: var(--accent-red);
+}
+
+.agent-status-dot.unknown {
+    background: #666;
+}
+
 .header-controls {
     display: flex;
     align-items: center;