[FEATURE] Expose session name to statusLine JSON input

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The statusLine feature receives JSON data via stdin, but the session/conversation name (set via /rename or automatically) is not included. Users who want to display the current chat name in their status bar cannot access it.

Use Case

Displaying the current conversation name in the status bar helps users:

• Quickly identify which conversation they're in
• Navigate multi-session workflows
• Maintain context when switching between tasks

Current Behavior

The statusLine JSON includes various fields, this critical one is missing:

• session_id (UUID)
• transcript_path (file path, often contains UUID)
• workspace, model, context_window, version

Proposed Solution

Add a session_name field to the statusLine JSON input that contains the human-readable name set via /rename (or assigned automatically).

```json
{
"session_id": "abc123...",
"session_name": "Status Bar adjustments", // <-- new field
"transcript_path": "...",
...
}

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_