Add config validation and dashboard

Add YAML config loading with validation, env overrides for secrets, and
a web dashboard exposing health, stats, and recent events.

docker_watcher.v

@@ -0,0 +1,75 @@
+module main
+
+import time
+$if linux || macos {
+	import net.unix
+	import os
+}
+import sources as _
+
+fn (mut app App) docker_watch_loop() {
+	$if linux || macos {
+		for {
+			for src in app.cfg.sources.docker {
+				for host in src.hosts {
+					app.watch_docker_host(src, host)
+				}
+			}
+			time.sleep(10 * time.second)
+		}
+	} $else {
+		app.logger.warn('docker', 'watch',
+			'Docker socket watching is only supported on Linux/macOS')
+		for {
+			time.sleep(60 * time.second)
+		}
+	}
+}
+
+$if linux || macos {
+	fn (mut app App) watch_docker_host(src _.DockerSource, host string) {
+		socket_path := host.replace('unix://', '')
+		if !os.exists(socket_path) {
+			app.logger.warn('docker', 'watch', 'socket not found: ${socket_path}')
+			return
+		}
+
+		mut conn := unix.connect_stream(socket_path) or {
+			app.logger.warn('docker', 'watch', 'failed to connect to ${socket_path}: ${err}')
+			return
+		}
+		defer {
+			conn.close() or {}
+		}
+
+		filters := build_docker_filters(src.events)
+		request := 'GET /events?filters=${filters} HTTP/1.1\r\nHost: localhost\r\n\r\n'
+		conn.write_string(request) or {
+			app.logger.warn('docker', 'watch', 'write error: ${err}')
+			return
+		}
+
+		mut buf := []u8{len: 4096}
+		for {
+			read := conn.read(mut buf) or { break }
+			if read <= 0 {
+				break
+			}
+			lines := buf[..read].bytestr().split_into_lines()
+			for line in lines {
+				if line.starts_with('{') {
+					event := sources.transform_docker_event(line, src, host) or { continue }
+					app.publish(event)
+				}
+			}
+		}
+	}
+
+	fn build_docker_filters(events []string) string {
+		mut parts := []string{}
+		for event in events {
+			parts << '"${event}":true'
+		}
+		return '{' + parts.join(',') + '}'
+	}
+}