feat: add terraform-local package type for local registry

- New package type "terraform-local" for hosting terraform providers
  without an upstream registry
- Upload via PUT /api/v2/remotes/{name}/files/{path}, returns 409 on
  duplicate (overwrites not allowed)
- Download via GET on same path, or via v1 proxy route
- Provider registers as fully immutable, no upstream rewriting
- v1 proxy handler serves local files directly for local repo types
- Database CRUD for local_files table

internal/database/local_files.go

@@ -0,0 +1,81 @@
+package database
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+type LocalFile struct {
+	ID          int64  `json:"id"`
+	RepoName    string `json:"repo_name"`
+	FilePath    string `json:"file_path"`
+	ContentHash string `json:"content_hash"`
+	CreatedAt   string `json:"created_at"`
+}
+
+var ErrAlreadyExists = fmt.Errorf("file already exists")
+
+func (db *DB) CreateLocalFile(ctx context.Context, repoName, filePath, contentHash string) error {
+	_, err := db.Pool.Exec(ctx, `
+		INSERT INTO local_files (repo_name, file_path, content_hash)
+		VALUES ($1, $2, $3)
+	`, repoName, filePath, contentHash)
+	if err != nil {
+		var pgErr *pgconn.PgError
+		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
+			return ErrAlreadyExists
+		}
+		return err
+	}
+	return nil
+}
+
+func (db *DB) GetLocalFile(ctx context.Context, repoName, filePath string) (*LocalFile, error) {
+	row := db.Pool.QueryRow(ctx, `
+		SELECT id, repo_name, file_path, content_hash, created_at
+		FROM local_files
+		WHERE repo_name = $1 AND file_path = $2
+	`, repoName, filePath)
+
+	var f LocalFile
+	if err := row.Scan(&f.ID, &f.RepoName, &f.FilePath, &f.ContentHash, &f.CreatedAt); err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &f, nil
+}
+
+func (db *DB) ListLocalFiles(ctx context.Context, repoName string, limit, offset int) ([]LocalFile, error) {
+	rows, err := db.Pool.Query(ctx, `
+		SELECT id, repo_name, file_path, content_hash, created_at
+		FROM local_files
+		WHERE repo_name = $1
+		ORDER BY file_path
+		LIMIT $2 OFFSET $3
+	`, repoName, limit, offset)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var files []LocalFile
+	for rows.Next() {
+		var f LocalFile
+		if err := rows.Scan(&f.ID, &f.RepoName, &f.FilePath, &f.ContentHash, &f.CreatedAt); err != nil {
+			return nil, err
+		}
+		files = append(files, f)
+	}
+	return files, rows.Err()
+}
+
+func (db *DB) DeleteLocalFile(ctx context.Context, repoName, filePath string) error {
+	_, err := db.Pool.Exec(ctx, `DELETE FROM local_files WHERE repo_name = $1 AND file_path = $2`, repoName, filePath)
+	return err
+}