Register sync DBs manually to fix dyalpm returning empty list

The dyalpm library's SyncDBs() returns an empty slice, causing packages
from official repos (extra, core, multilib) to not be found. This fix
manually registers each repo after getting an empty result.

openspec/changes/fix-sync-dbs-not-loaded/tasks.md

@@ -1,10 +1,10 @@
 ## 1. Implement sync DB registration
 
-- [ ] 1.1 Modify Pac struct to include a method for registering sync DBs
-- [ ] 1.2 In New(), after getting empty syncDBs from handle, loop through ["core", "extra", "multilib"] and call RegisterSyncDB for each
-- [ ] 1.3 Filter out repos that have no packages (not configured in pacman.conf)
+- [x] 1.1 Modify Pac struct to include a method for registering sync DBs
+- [x] 1.2 In New(), after getting empty syncDBs from handle, loop through ["core", "extra", "multilib"] and call RegisterSyncDB for each
+- [x] 1.3 Filter out repos that have no packages (not configured in pacman.conf)
 
 ## 2. Test the fix
 
-- [ ] 2.1 Run `./declpac --dry-run --state <(echo "cmake")` and verify it resolves cmake from extra repo
-- [ ] 2.2 Test with other official repo packages (e.g., "git" from extra, "base" from core)
+- [x] 2.1 Run `./declpac --dry-run --state <(echo "cmake")` and verify it resolves cmake from extra repo
+- [x] 2.2 Test with other official repo packages (e.g., "git" from extra, "base" from core)

pkg/pacman/pacman.go

@@ -50,6 +50,14 @@ func New() (*Pac, error) {
 		return nil, fmt.Errorf("failed to get sync databases: %w", err)
 	}
 
+	if len(syncDBs) == 0 {
+		syncDBs, err = registerSyncDBs(handle)
+		if err != nil {
+			handle.Release()
+			return nil, fmt.Errorf("failed to register sync databases: %w", err)
+		}
+	}
+
 	fmt.Fprintf(os.Stderr, "[debug] New: done (%.2fs)\n", time.Since(start).Seconds())
 	return &Pac{
 		aurCache: make(map[string]AURPackage),
@@ -66,6 +74,33 @@ func (p *Pac) Close() error {
 	return nil
 }
 
+func registerSyncDBs(handle dyalpm.Handle) ([]dyalpm.Database, error) {
+	fmt.Fprintf(os.Stderr, "[debug] registerSyncDBs: starting...\n")
+
+	repos := []string{"core", "extra", "multilib"}
+	var dbs []dyalpm.Database
+
+	for _, repo := range repos {
+		db, err := handle.RegisterSyncDB(repo, 0)
+		if err != nil {
+			continue
+		}
+
+		count := 0
+		db.PkgCache().ForEach(func(pkg dyalpm.Package) error {
+			count++
+			return nil
+		})
+
+		if count > 0 {
+			dbs = append(dbs, db)
+		}
+	}
+
+	fmt.Fprintf(os.Stderr, "[debug] registerSyncDBs: done (%d dbs)\n", len(dbs))
+	return dbs, nil
+}
+
 type PackageInfo struct {
 	Name      string
 	InAUR     bool