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.

specs/008-ai-rename-prompt/data-model.md

@@ -0,0 +1,99 @@
+# Data Model: AI-Assisted Rename Prompting
+
+## AiRenamePrompt
+- **Fields**
+  - `WorkingDir` (string; absolute path)
+  - `SampleFiles` ([]PromptSample)
+  - `TotalCount` (int)
+  - `SequenceRule` (SequenceRuleConfig)
+  - `NamingPolicies` (NamingPolicyConfig)
+  - `BannedTerms` ([]string)
+  - `Metadata` (map[string]string; includes CLI version, timestamp)
+- **Relationships**: Built from traversal summary; sent to Genkit workflow.
+- **Validations**: Require ≥1 sample, forbid empty banned terms, limit payload to ≤2 MB serialized.
+
+### PromptSample
+- **Fields**
+  - `OriginalName` (string)
+  - `SizeBytes` (int64)
+  - `Extension` (string)
+  - `PathDepth` (int)
+
+### SequenceRuleConfig
+- **Fields**
+  - `Style` (enum: `prefix`, `suffix`)
+  - `Width` (int)
+  - `Start` (int)
+  - `Separator` (string)
+
+### NamingPolicyConfig
+- **Fields**
+  - `Prefix` (string)
+  - `Casing` (enum: `kebab`, `snake`, `camel`, `pascal`, `title`)
+  - `AllowSpaces` (bool)
+  - `KeepOriginalOrder` (bool)
+  - `ForbiddenTokens` ([]string)
+
+## AiRenameResponse
+- **Fields**
+  - `Items` ([]AiRenameItem)
+  - `Warnings` ([]string)
+  - `PromptHash` (string)
+  - `Model` (string)
+- **Relationships**: Parsed from Genkit output; feeds validation pipeline.
+- **Validations**: Items length must equal scoped candidate count; `Original` names must match traversal list; `Proposed` must be unique.
+
+### AiRenameItem
+- **Fields**
+  - `Original` (string; relative path)
+  - `Proposed` (string; sanitized stem + extension)
+  - `Sequence` (int)
+  - `Notes` (string; optional reasoning)
+
+## AiRenamePlan
+- **Fields**
+  - `Candidates` ([]PlanEntry)
+  - `Conflicts` ([]PlanConflict)
+  - `Policies` (NamingPolicyConfig)
+  - `SequenceAppliedWidth` (int)
+  - `Warnings` ([]string)
+- **Relationships**: Created post-validation for preview/apply; persisted to ledger metadata.
+- **Validations**: Enforce contiguous sequences, ensure sanitized stems non-empty, confirm banned tokens absent.
+
+### PlanEntry
+- **Fields**
+  - `OriginalPath` (string)
+  - `ProposedPath` (string)
+  - `Sequence` (int)
+  - `Status` (enum: `pending`, `edited`, `skipped`, `unchanged`)
+  - `SanitizedSegments` ([]string)
+
+### PlanConflict
+- **Fields**
+  - `OriginalPath` (string)
+  - `Issue` (enum: `duplicate`, `collision`, `policy_violation`, `missing_sequence`)
+  - `Details` (string)
+
+## AiRenameLedgerMetadata
+- **Fields**
+  - `PromptHash` (string)
+  - `ResponseHash` (string)
+  - `Model` (string)
+  - `Policies` (NamingPolicyConfig)
+  - `BatchSize` (int)
+  - `AppliedAt` (time.Time)
+- **Relationships**: Stored under `Entry.Metadata["ai"]` when applying rename batch; consumed by undo for auditing.
+
+## GenkitWorkflowConfig
+- **Fields**
+  - `Endpoint` (string; local or remote URL)
+  - `Timeout` (Duration)
+  - `RetryPolicy` (RetryPolicy)
+  - `ApiKeyRef` (string; environment variable name mapping to `$HOME/.config/.renamer/{name}` token file)
+
+### RetryPolicy
+- **Fields**
+  - `MaxAttempts` (int)
+  - `BackoffInitial` (Duration)
+  - `BackoffMultiplier` (float64)
+  - `FallbackModel` (string; optional)