Add model recommendation and runtime health UX

[FuJacob]

Problem

Users can choose between tabby-fast-1, tabby-balanced-1, and tabby-depth-1, but the product does not clearly explain the speed, quality, memory, and readiness tradeoffs. When the runtime fails or is loading, users also need better visibility into what is happening.

Goal

Improve model selection and runtime status UX so users can choose the right model and understand whether Tabby is ready to suggest.

Proposed Scope

• Add concise recommendation copy for each curated model:
  • tabby-fast-1: fastest, lowest memory, lighter quality.
  • tabby-balanced-1: default/recommended balance.
  • tabby-depth-1: highest quality/deeper reasoning, larger download and memory use.
• Show installed size or approximate size in model rows.
• Show selected model state clearly.
• Show delete actions for removable local models.
• Show runtime readiness, loading state, and last runtime error near model selection.
• Make Apple Intelligence availability and Open Source runtime health feel comparable in Settings.

Acceptance Criteria

• Each curated model has user-facing recommendation copy.
• The selected model is visually obvious in Settings and menu bar surfaces.
• Installed/removable models show delete affordances where appropriate.
• Runtime state explains loading, ready, missing model, and failed states clearly.
• Users can understand why Open Source suggestions are unavailable without reading logs.

Open Questions

• Should tabby-balanced-1 be explicitly labeled recommended?
• Should model health live in Settings only, menu bar only, or both?
• Should we show memory estimates, download size, or both?

[FuJacob]

Closing — this references the old three-model catalog (tabby-fast-1, tabby-balanced-1, tabby-depth-1) which no longer exists. PR #124 simplified to two models (tabby-fast, tabby-quality) with clear naming.

The runtime-health UX portion (loading/ready/failed states visible in menu bar) is still partially relevant but should be a fresh, narrower issue if someone wants to pick it up.