fix(cli-workflow): complete step read command implementation

Implements the `uwf step read` command to render a single step's turns
as human-readable markdown with quota enforcement.

Changes:
- Implement cmdStepRead() in step.ts with quota enforcement
  - Renders step metadata (hash, role, agent)
  - Loads and formats turns from detail node
  - Enforces quota by selecting most recent turns
  - Always shows at least one turn even if it exceeds quota
  - Gracefully handles steps with no detail or no turns
- Register `step read` command in cli.ts with --quota flag (default 4000)
- Add comprehensive test suite in step-read.test.ts (6 tests covering
  basic functionality, quota enforcement, edge cases, and special chars)
- Update README.md CLI Reference table to include `step read`
- Update package-level README.md with command documentation and example

Closes #484

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

README.md

@@ -80,7 +80,7 @@ Global options: `-V, --version`, `--format <json|yaml>`, `-h, --help`.
 | Group | Commands |
 |-------|----------|
 | **thread** | `start`, `exec`, `show`, `list`, `stop`, `cancel`, `read` |
-| **step** | `list`, `show`, `fork` |
+| **step** | `list`, `show`, `read`, `fork` |
 | **workflow** | `add`, `show`, `list` |
 | **cas** | `get`, `put`, `put-text`, `has`, `refs`, `walk`, `reindex`, `schema list`, `schema get` |
 | **setup** | Interactive or `--provider`, `--base-url`, `--api-key`, `--model`, `--agent` |