Reorganize repo: backend/, deploy/, docs/ layout + AGENTS.md

Restructure the monorepo into clear top-level directories:
- backend/: Go module root (cmd, internal, pkg, configs, migrations,
  docs/swagger, scripts, tests, go.mod, Makefile, .air.toml)
- deploy/: Docker (Dockerfile, docker-compose*), quickstart, fluentd
- docs/: project documentation + reports/ (moved from repo root)
- AGENTS.md: new AI coding-agent guide at repo root

Update all references to the new layout:
- Dockerfile: COPY backend/go.mod, COPY backend/ (context = repo root)
- docker-compose files: context ../.., dockerfile deploy/docker/Dockerfile,
  env_file ../../.env, volume mounts ../../backend:/app
- deploy/quickstart/compose.yaml: dockerfile deploy/docker/Dockerfile
- CI: working-directory: backend for go commands, file deploy/docker/Dockerfile,
  coverage path backend/coverage.out, health_check backend/scripts/
- backend/Makefile: docker target uses -f ../deploy/docker/Dockerfile ../
- README: architecture tree, quickstart, config paths updated

Move root stray scripts (rename_models.*, run_m11_tests.sh, verify_build.sh,
gorm_bool_main.go) to backend/scripts/legacy/. All moves via git mv to
preserve history. Build, vet, SQLite tests, and docker compose config verified.

backend/internal/middleware/cors_logger.go

@@ -0,0 +1,42 @@
+package middleware
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// CORSMiddleware adds permissive CORS headers for development.
+func CORSMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Header("Access-Control-Allow-Origin", "*")
+		c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, PATCH, DELETE, OPTIONS")
+		c.Header("Access-Control-Allow-Headers", "Origin, Content-Type, Accept, Authorization")
+		c.Header("Access-Control-Max-Age", "86400")
+		c.Header("Access-Control-Allow-Credentials", "true")
+
+		if c.Request.Method == "OPTIONS" {
+			c.AbortWithStatus(204)
+			return
+		}
+
+		c.Next()
+	}
+}
+
+// RequestLoggerMiddleware logs method, path, status, and latency.
+func RequestLoggerMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+		path := c.Request.URL.Path
+
+		c.Next()
+
+		latency := time.Since(start)
+		status := c.Writer.Status()
+		method := c.Request.Method
+
+		fmt.Fprintf(gin.DefaultWriter, "%s %s %d %v\n", method, path, status, latency)
+	}
+}