feat(logging): integrate slog logging with env control and request/sync tracing

- Configure structured slog logger in cmd/server/main.go via LOG_LEVEL and DEBUG env vars
- Add HTTP API request logging middleware in internal/api/ with status and duration_ms
- Add WebSocket join/leave, event reception, and debounced SQLite flush tracing in docroom
- Document LOG_LEVEL and DEBUG settings in .env.example, compose.yaml, and docker-compose.yml

internal/config/config_test.go

@@ -0,0 +1,58 @@
+package config
+
+import (
+	"log/slog"
+	"os"
+	"testing"
+)
+
+func TestConfigLogLevelAndDebug(t *testing.T) {
+	os.Setenv("PORT", "9090")
+	defer os.Unsetenv("PORT")
+
+	// 1. Default info
+	os.Unsetenv("LOG_LEVEL")
+	os.Unsetenv("DEBUG")
+	cfg := Load()
+	if cfg.SlogLevel() != slog.LevelInfo {
+		t.Fatalf("expected LevelInfo, got %v", cfg.SlogLevel())
+	}
+
+	// 2. LOG_LEVEL=debug
+	os.Setenv("LOG_LEVEL", "debug")
+	cfg = Load()
+	if cfg.SlogLevel() != slog.LevelDebug {
+		t.Fatalf("expected LevelDebug, got %v", cfg.SlogLevel())
+	}
+
+	// 3. LOG_LEVEL=warn
+	os.Setenv("LOG_LEVEL", "warn")
+	cfg = Load()
+	if cfg.SlogLevel() != slog.LevelWarn {
+		t.Fatalf("expected LevelWarn, got %v", cfg.SlogLevel())
+	}
+
+	// 4. LOG_LEVEL=error
+	os.Setenv("LOG_LEVEL", "error")
+	cfg = Load()
+	if cfg.SlogLevel() != slog.LevelError {
+		t.Fatalf("expected LevelError, got %v", cfg.SlogLevel())
+	}
+
+	// 5. DEBUG=true overrides LOG_LEVEL
+	os.Setenv("LOG_LEVEL", "error")
+	os.Setenv("DEBUG", "true")
+	cfg = Load()
+	if cfg.SlogLevel() != slog.LevelDebug {
+		t.Fatalf("expected LevelDebug when DEBUG=true, got %v", cfg.SlogLevel())
+	}
+
+	// 6. DEBUG=1 overrides LOG_LEVEL
+	os.Setenv("DEBUG", "1")
+	cfg = Load()
+	if cfg.SlogLevel() != slog.LevelDebug {
+		t.Fatalf("expected LevelDebug when DEBUG=1, got %v", cfg.SlogLevel())
+	}
+	os.Unsetenv("DEBUG")
+	os.Unsetenv("LOG_LEVEL")
+}