feat(cli): add preset create and delete commands

[admin86888]

Summary

Adds the missing preset CRUD operations to skills-manager-cli:

• presets create <name> [--description ...] [--icon ...]
• presets delete <reference>

This resubmission is intentionally limited to CLI preset create/delete and the shared core logic required by the GUI and CLI.

Implementation

• Extracts preset persistence into the shared scenario_service::create_preset.
• Moves the complete preset deletion flow into scenario_service::delete_preset.
• Updates the GUI create/delete commands to use the shared core functions.
• Adds structured JSON output for CLI deletion results.
• Trims preset names and rejects blank names.

Behavior

Create

The GUI continues to activate a newly created preset immediately.

CLI creation intentionally leaves the new preset inactive. This allows automation to create a preset, populate it with presets add-skill, and explicitly activate it when ready:

skills-manager-cli presets create Automation
skills-manager-cli presets add-skill Automation skill-a skill-b
skills-manager-cli presets apply Automation

This behavior is documented in presets create --help, and the command output reports "active": false.

### Delete

GUI and CLI now share the same deletion behavior:

- If the deleted preset is inactive, the current active preset is unchanged.
- If it is active, its synced targets are removed first.
- The first remaining preset in persisted order (sort_order, then created_at) becomes active and is synced.
- If no presets remain, the active preset is cleared.

The CLI no longer applies a separate default_scenario replacement preference during deletion.

## Scope

This PR only changes:

- src-tauri/src/bin/skills-manager-cli.rs
- src-tauri/src/commands/presets.rs
- src-tauri/src/core/scenario_service.rs

It does not include UI scrolling changes, build scripts, documentation, README, dependency, or CHANGELOG changes. CHANGELOG updates are left to the existing release:prepare workflow.

## Testing

- cargo test
    - 398 library tests passed
    - 3 CLI tests passed

- npm run lint
- npm run build
- Manual CLI smoke tests covering:
    - create without activation
    - explicit apply
    - active and inactive deletion
    - replacement preset selection
    - name trimming
    - blank-name rejection

The pre-push verification hook also completed successfully.

[quoxientzero]

Glad this feature is coming, will be on the lookout!