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

intercept_agent.cfg

@@ -0,0 +1,59 @@
+# =============================================================================
+# INTERCEPT AGENT CONFIGURATION
+# =============================================================================
+# This file configures the Intercept remote agent.
+# Copy this file and customize for your deployment.
+
+[agent]
+# Agent name (used to identify this node in the controller)
+# Default: system hostname
+name = sensor-node-1
+
+# HTTP server port
+# Default: 8020
+port = 8020
+
+# Comma-separated list of allowed client IPs (empty = allow all)
+# Example: 192.168.1.100, 192.168.1.101, 10.0.0.0/8
+allowed_ips =
+
+# Enable CORS headers for browser-based clients
+# Default: false
+allow_cors = false
+
+
+[controller]
+# Controller URL for push mode
+# Example: http://192.168.1.100:5050
+url =
+
+# API key for controller authentication (shared secret)
+api_key =
+
+# Enable automatic push of scan data to controller
+# Default: false
+push_enabled = false
+
+# Push interval in seconds (minimum time between pushes)
+# Default: 5
+push_interval = 5
+
+
+[modes]
+# Enable/disable specific modes on this agent
+# Set to false to disable a mode even if tools are available
+# Default: all true
+
+pager = true
+sensor = true
+adsb = true
+ais = true
+acars = true
+aprs = true
+wifi = true
+bluetooth = true
+dsc = true
+rtlamr = true
+tscm = true
+satellite = true
+listening_post = true