feat: Production readiness improvements for WHOOSH council formation

Major security, observability, and configuration improvements:

## Security Hardening
- Implemented configurable CORS (no more wildcards)
- Added comprehensive auth middleware for admin endpoints
- Enhanced webhook HMAC validation
- Added input validation and rate limiting
- Security headers and CSP policies

## Configuration Management
- Made N8N webhook URL configurable (WHOOSH_N8N_BASE_URL)
- Replaced all hardcoded endpoints with environment variables
- Added feature flags for LLM vs heuristic composition
- Gitea fetch hardening with EAGER_FILTER and FULL_RESCAN options

## API Completeness
- Implemented GetCouncilComposition function
- Added GET /api/v1/councils/{id} endpoint
- Council artifacts API (POST/GET /api/v1/councils/{id}/artifacts)
- /admin/health/details endpoint with component status
- Database lookup for repository URLs (no hardcoded fallbacks)

## Observability & Performance
- Added OpenTelemetry distributed tracing with goal/pulse correlation
- Performance optimization database indexes
- Comprehensive health monitoring
- Enhanced logging and error handling

## Infrastructure
- Production-ready P2P discovery (replaces mock implementation)
- Removed unused Redis configuration
- Enhanced Docker Swarm integration
- Added migration files for performance indexes

## Code Quality
- Comprehensive input validation
- Graceful error handling and failsafe fallbacks
- Backwards compatibility maintained
- Following security best practices

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

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

vendor/github.com/go-chi/chi/v5/middleware/sunset.go

@@ -0,0 +1,25 @@
+package middleware
+
+import (
+	"net/http"
+	"time"
+)
+
+// Sunset set Deprecation/Sunset header to response
+// This can be used to enable Sunset in a route or a route group
+// For more: https://www.rfc-editor.org/rfc/rfc8594.html
+func Sunset(sunsetAt time.Time, links ...string) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if !sunsetAt.IsZero() {
+				w.Header().Set("Sunset", sunsetAt.Format(http.TimeFormat))
+				w.Header().Set("Deprecation", sunsetAt.Format(http.TimeFormat))
+
+				for _, link := range links {
+					w.Header().Add("Link", link)
+				}
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}