fix(cli): resolve lint errors and unused imports (#463)

Fix all lint errors flagged by biome check to ensure clean codebase.

## Changes

### Removed Unused Imports
- `packages/cli-workflow/src/commands/thread.ts`:
  - Removed `StartEntry` (moved to step.ts)
  - Removed `StepEntry` (moved to step.ts)
  - Removed `ThreadForkOutput` (moved to step.ts)
  - Removed `ThreadStepsOutput` (moved to step.ts)

- `packages/cli-workflow/src/cli.ts`:
  - Removed unused `yamlStringify` import from yaml package

### Fixed Unused Parameter
- `packages/cli-workflow/src/commands/step.ts`:
  - Prefixed unused `before` parameter with underscore in `cmdStepRead`
  - Parameter is part of the function signature for future use (awaiting #462)

### Fixed Import Order
- `packages/cli-workflow/src/__tests__/thread.test.ts`:
  - Reordered imports to follow biome's organization rules
  - Moved cmdStepShow import before cmdThreadRead imports

## Test Results
- ✅ `bun run check` passes (typecheck + lint + log tags)
- ✅ All 124 tests passing
- ✅ Build completes successfully

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/cli-workflow/src/cli.ts

@@ -2,7 +2,6 @@
 
 import type { CasRef, ThreadId } from "@uncaged/workflow-protocol";
 import { Command } from "commander";
-import { stringify as yamlStringify } from "yaml";
 import {
   cmdCasGet,
   cmdCasHas,
@@ -100,9 +99,7 @@ workflow
     });
   });
 
-const thread = program
-  .command("thread")
-  .description("Thread execution (layer 2: instances)");
+const thread = program.command("thread").description("Thread execution (layer 2: instances)");
 
 thread
   .command("start")