feat(ui): file browser and connection string builder dialogs (#44)

Enter on File Path inputs opens a file browser (load/save, extension
filter, hidden toggle, overwrite confirm). Enter on Connection String
inputs opens a builder for PostgreSQL, MSSQL and SQLite with masked
password/preview, parsing and optional connection test.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pkg/ui/filebrowser.go

@@ -0,0 +1,134 @@
+package ui
+
+import (
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// FileEntry is a single row in the file browser.
+type FileEntry struct {
+	Name  string
+	IsDir bool
+}
+
+// formatExtensions maps a UI format name to the file extensions it reads or writes.
+var formatExtensions = map[string][]string{
+	"dbml":    {".dbml"},
+	"dctx":    {".dctx"},
+	"drawdb":  {".json"},
+	"graphql": {".graphql", ".gql"},
+	"json":    {".json"},
+	"yaml":    {".yaml", ".yml"},
+	"gorm":    {".go"},
+	"bun":     {".go"},
+	"drizzle": {".ts"},
+	"prisma":  {".prisma"},
+	"typeorm": {".ts"},
+	"pgsql":   {".sql"},
+	"sqlite":  {".db", ".sqlite", ".sqlite3"},
+}
+
+// directoryFormats are formats whose reader/writer accepts a directory.
+var directoryFormats = map[string]bool{
+	"gorm": true, "bun": true, "drizzle": true, "typeorm": true,
+}
+
+// FormatExtensions returns the extensions for a format, or nil (no filter) if unknown.
+func FormatExtensions(format string) []string {
+	return formatExtensions[format]
+}
+
+// IsDirectoryFormat reports whether a format can be loaded from or saved to a directory.
+func IsDirectoryFormat(format string) bool {
+	return directoryFormats[format]
+}
+
+// ExpandHome replaces a leading ~ with the user's home directory.
+func ExpandHome(p string) string {
+	if strings.HasPrefix(p, "~") {
+		if home, err := os.UserHomeDir(); err == nil {
+			return filepath.Join(home, p[1:])
+		}
+	}
+	return p
+}
+
+// MatchesExtension reports whether name has one of exts (case-insensitive).
+// An empty extension list matches everything.
+func MatchesExtension(name string, exts []string) bool {
+	if len(exts) == 0 {
+		return true
+	}
+	ext := strings.ToLower(filepath.Ext(name))
+	for _, e := range exts {
+		if strings.ToLower(e) == ext {
+			return true
+		}
+	}
+	return false
+}
+
+// ListDir returns the entries of dir: directories first, then files that match
+// exts, each group sorted case-insensitively. Hidden (dot) entries are skipped
+// unless showHidden is set.
+func ListDir(dir string, exts []string, showHidden bool) ([]FileEntry, error) {
+	items, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	var dirs, files []FileEntry
+	for _, item := range items {
+		name := item.Name()
+		if !showHidden && strings.HasPrefix(name, ".") {
+			continue
+		}
+		isDir := item.IsDir()
+		if !isDir && item.Type()&os.ModeSymlink != 0 {
+			// Follow symlinks so links to directories are navigable.
+			if info, err := os.Stat(filepath.Join(dir, name)); err == nil {
+				isDir = info.IsDir()
+			}
+		}
+		if isDir {
+			dirs = append(dirs, FileEntry{Name: name, IsDir: true})
+		} else if MatchesExtension(name, exts) {
+			files = append(files, FileEntry{Name: name})
+		}
+	}
+
+	byName := func(s []FileEntry) {
+		sort.Slice(s, func(i, j int) bool {
+			return strings.ToLower(s[i].Name) < strings.ToLower(s[j].Name)
+		})
+	}
+	byName(dirs)
+	byName(files)
+	return append(dirs, files...), nil
+}
+
+// ResolveStart works out where the browser should open for the current input
+// value. It returns the directory to show and, if the input named a file, its
+// base name. Falls back to the working directory.
+func ResolveStart(input string) (dir, name string) {
+	input = strings.TrimSpace(input)
+	if input != "" {
+		p := ExpandHome(input)
+		if abs, err := filepath.Abs(p); err == nil {
+			p = abs
+		}
+		if info, err := os.Stat(p); err == nil && info.IsDir() {
+			return p, ""
+		}
+		if info, err := os.Stat(filepath.Dir(p)); err == nil && info.IsDir() {
+			return filepath.Dir(p), filepath.Base(p)
+		}
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		wd = "."
+	}
+	return wd, ""
+}