feat(commands): slash commands should directly apply settings, not just display them

[akougkas]

Problem

Every configurable slash command is display-only:

• /modes build shows "To switch to Build, ask Panos: 'switch to build mode'"
• /safety suggest shows "To apply suggest, ask Panos: 'change safety to suggest'"
• /reasoning high shows "To apply high, ask Panos: 'set reasoning to high'"
• /models <ref> shows "To switch to X, ask Panos: 'use X'"
• /preset <name> shows preset config but does not apply it
• /theme <name> shows theme list but does not switch

Users must either use keyboard shortcuts (only 3 exist) or ask the LLM to call pan_apply_config. This creates a slow feedback loop for simple operations and couples basic configuration to LLM reliability.

The readOnlyBanner() function explicitly states: "Read-only view. Ask Panos to change any setting, or use keyboard shortcuts."

Meanwhile, the keyboard shortcuts DO apply changes directly: Shift+Tab switches mode, Ctrl+Y switches safety. This inconsistency means commands are second-class to shortcuts.

Audit Reference

AUDIT-ISSUES.md: F1, C1, C10

Objective

Make slash commands direct-action when given arguments. Display-only when called without arguments.

Deliverables

• /modes <mode> directly calls setCurrentMode + setActiveTools + emits CONFIG_CHANGED
• /safety <level> directly sets PANCODE_SAFETY + persists + emits CONFIG_CHANGED
• /reasoning <level> directly applies reasoning level
• /theme <name> directly switches theme
• /preset <name> applies preset at runtime (sets model, worker, scout, reasoning, safety)
• /models <ref> calls pi.setModel() directly when exact match found
• All commands remain display-only when called without arguments (current behavior preserved)