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/conflicts.go

@@ -0,0 +1,67 @@
+package plan
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/rogeecn/renamer/internal/ai/prompt"
+)
+
+// Conflict describes an issue detected in an AI rename plan.
+type Conflict struct {
+	OriginalPath string
+	Issue        string
+	Details      string
+}
+
+func detectConflicts(items []prompt.RenameItem) []Conflict {
+	conflicts := make([]Conflict, 0)
+
+	if len(items) == 0 {
+		return conflicts
+	}
+
+	targets := make(map[string][]prompt.RenameItem)
+	sequences := make([]int, 0, len(items))
+
+	for _, item := range items {
+		key := strings.ToLower(strings.TrimSpace(item.Proposed))
+		if key != "" {
+			targets[key] = append(targets[key], item)
+		}
+		if item.Sequence > 0 {
+			sequences = append(sequences, item.Sequence)
+		}
+	}
+
+	for _, entries := range targets {
+		if len(entries) <= 1 {
+			continue
+		}
+		for _, entry := range entries {
+			conflicts = append(conflicts, Conflict{
+				OriginalPath: entry.Original,
+				Issue:        "duplicate_target",
+				Details:      fmt.Sprintf("target %q is used by multiple entries", entries[0].Proposed),
+			})
+		}
+	}
+
+	if len(sequences) > 0 {
+		sort.Ints(sequences)
+		expected := 1
+		for _, seq := range sequences {
+			if seq != expected {
+				conflicts = append(conflicts, Conflict{
+					Issue:   "sequence_gap",
+					Details: fmt.Sprintf("expected sequence %d but found %d", expected, seq),
+				})
+				expected = seq
+			}
+			expected++
+		}
+	}
+
+	return conflicts
+}