feat: rewrite gh-commit in Go with local Ollama backend

Replaces the Python/Crush/DuckDB implementation with a CGO-free Go binary:
cobra CLI, modernc.org/sqlite storage, huh/lipgloss UI, and speed-tuned raw
/api/generate calls (think:false, keep_alive, capped num_predict) against a
local qwen3.5:2b. Ships as a gh extension via cli/gh-extension-precompile.

cmd/migrate.go

@@ -0,0 +1,93 @@
+package cmd
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/BurntSushi/toml"
+
+	"github.com/prdlk/gh-commit/internal/ai"
+	"github.com/prdlk/gh-commit/internal/gitx"
+	"github.com/prdlk/gh-commit/internal/ui"
+)
+
+// archiveMigrated renames a consumed legacy file to *.migrated.<timestamp>.
+func archiveMigrated(path string) (string, error) {
+	backup := path + ".migrated." + time.Now().Format("20060102_150405")
+	return backup, os.Rename(path, backup)
+}
+
+// migrateTOML imports scopes from .github/Repo.toml.
+func migrateTOML(repoPath, repoName, tomlPath string) bool {
+	ui.Warnf("↻ Migrating .github/Repo.toml → database")
+	var doc struct {
+		Scopes map[string]any `toml:"scopes"`
+	}
+	if _, err := toml.DecodeFile(tomlPath, &doc); err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	scopes := ai.CoerceScopeMap(doc.Scopes)
+	if scopes == nil {
+		scopes = map[string][]string{}
+	}
+	if err := store.SaveScopes(repoPath, repoName, scopes, gitx.GitignoreHash(repoPath)); err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	backup, err := archiveMigrated(tomlPath)
+	if err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	ui.Dimf("  Archived: %s", backup)
+	return true
+}
+
+// migrateJSON imports scopes from .github/scopes.json
+// (an array of {"scope": ..., "path": ...} entries).
+func migrateJSON(repoPath, repoName, jsonPath string) bool {
+	ui.Warnf("↻ Migrating .github/scopes.json → database")
+	data, err := os.ReadFile(jsonPath)
+	if err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	var entries []struct {
+		Scope string `json:"scope"`
+		Path  string `json:"path"`
+	}
+	if err := json.Unmarshal(data, &entries); err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	scopes := map[string][]string{}
+	for _, e := range entries {
+		scopes[e.Scope] = append(scopes[e.Scope], e.Path)
+	}
+	if err := store.SaveScopes(repoPath, repoName, scopes, gitx.GitignoreHash(repoPath)); err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	backup, err := archiveMigrated(jsonPath)
+	if err != nil {
+		ui.Errorf("Migration failed: %s", err)
+		return false
+	}
+	ui.Dimf("  Archived: %s", backup)
+	return true
+}
+
+// migrateLegacy imports whichever legacy config file exists, if any.
+func migrateLegacy(repoPath string) bool {
+	repoName := filepath.Base(repoPath)
+	if tomlPath := filepath.Join(repoPath, ".github", "Repo.toml"); fileExists(tomlPath) {
+		return migrateTOML(repoPath, repoName, tomlPath)
+	}
+	if jsonPath := filepath.Join(repoPath, ".github", "scopes.json"); fileExists(jsonPath) {
+		return migrateJSON(repoPath, repoName, jsonPath)
+	}
+	return false
+}