feat(tui): add /skills command to display available skills

[narcilee7]

Related Issue

 N/A — small user-facing feature requested directly by maintainer.                                                                                                                                   

Problem

 Users currently have no built-in way to discover which skills are loaded in the active session. While individual `skill:*` slash commands are generated dynamically, there is no overview listing to help users understand what skills are available, where they come from, or what they do.

What changed

 - Added `/skills` built-in slash command** (`apps/kimi-code/src/tui/commands/registry.ts`).                                                                                                       
 - Added `showSkills()` handler** in `kimi-tui.ts` that fetches `session.listSkills()` and renders a panel into the transcript.                                                                    
 - Added `skills-panel.ts`** component that builds the report lines:                                                                                                                               
   - Skills are grouped by source (`Built-in`, `Project`, `User`, `Extra`) in a fixed order.                                                                                                         
   - A single global header (`Name`, `Type`, `Description`) is rendered at the top.                                                                                                                  
   - Column widths (`Name` and `Type`) are computed globally across all skills so that rows align cleanly even when different groups contain skills of varying name lengths.                         
   - Data rows are indented under their group label for visual hierarchy.                                                                                                                            
   - Empty groups are skipped entirely, keeping the output compact.                                                                                                                                  
 - The rendering reuses the existing `UsagePanelComponent` pattern (same as `/mcp`, `/usage`, `/status`), so the visual style stays consistent with the rest of the TUI.                             
 - Added a changeset for `@moonshot-ai/kimi-code` (`minor` bump) since this is a new backwards-compatible user-facing feature.                                                                       
                                                                                                                                                                                                     ## Why this approach                                                                                                                                                                                
                                                                                                                                                                                                     
 - **Follows existing conventions**: `/mcp`, `/usage`, and `/status` all use `UsagePanelComponent` + a dedicated `build*Lines` helper. `skills-panel.ts` mirrors that structure exactly.             
 - **Minimal TUI integration**: Only touches `registry.ts` (command registration), `kimi-tui.ts` (dispatch + handler), and a new panel file. No changes to core skill loading or SDK types.          
 - **Compact and scannable**: Grouping by source lets users quickly distinguish built-in skills from project-local or user-level ones. Global column alignment makes the table easy to scan.         

Checklist

 - [x] I have read the [CONTRIBUTING](https://github.com/MoonshotAI/kimi-code/blob/main/CONTRIBUTING.md) document.                                                                                   
 - [x] I have linked a related issue, or explained the problem above.                                                                                                                                
 - [x] I have added tests that prove my feature works. *(TUI panel rendering is not currently covered by unit tests; follows the same untested pattern as `/mcp` and `/usage` panels.)*              
 - [x] Ran `gen-changesets` skill, or this PR needs no changeset.                                                                                                                                    
 - [x] Ran `gen-docs` skill, or this PR needs no doc update. *(No user-facing docs change required for a single new slash command; inline help is self-documenting via the command registry.)*       

[changeset-bot]

🦋 Changeset detected

Latest commit: 116a264

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Minor

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