feat: implement AI-assisted rename prompting feature

- Added data model for AI-assisted renaming including structures for prompts, responses, and policies.
- Created implementation plan detailing the integration of Google Genkit into the CLI for renaming tasks.
- Developed quickstart guide for setting up and using the new AI rename functionality.
- Documented research decisions regarding Genkit orchestration and prompt composition.
- Established tasks for phased implementation, including setup, foundational work, and user stories.
- Implemented contract tests to ensure AI rename policies and ledger metadata are correctly applied.
- Developed integration tests for validating AI rename flows, including preview, apply, and undo functionalities.
- Added tooling to pin Genkit dependency for consistent builds.

internal/ai/plan/editor.go

@@ -0,0 +1,39 @@
+package plan
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+
+	"github.com/rogeecn/renamer/internal/ai/prompt"
+)
+
+// SaveResponse writes the AI rename response to disk for later editing.
+func SaveResponse(path string, resp prompt.RenameResponse) error {
+	data, err := json.MarshalIndent(resp, "", "  ")
+	if err != nil {
+		return fmt.Errorf("marshal ai plan: %w", err)
+	}
+	if err := os.WriteFile(path, append(data, '\n'), 0o644); err != nil {
+		return fmt.Errorf("write ai plan %s: %w", path, err)
+	}
+	return nil
+}
+
+// LoadResponse reads an edited AI rename response from disk.
+func LoadResponse(path string) (prompt.RenameResponse, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			return prompt.RenameResponse{}, fmt.Errorf("plan file %s not found", path)
+		}
+		return prompt.RenameResponse{}, fmt.Errorf("read plan file %s: %w", path, err)
+	}
+	var resp prompt.RenameResponse
+	if err := json.Unmarshal(data, &resp); err != nil {
+		return prompt.RenameResponse{}, fmt.Errorf("parse plan file %s: %w", path, err)
+	}
+	return resp, nil
+}