feat(macos): Lattice app v1 (Models + Chat)

[ohdearquant]

Summary

First release scope of the Lattice macOS app. This PR introduces the app to main in a deliberately narrow form — Models + Chat only — the two surfaces that work end to end against the engine binaries already on main.

Sliced from the LoRA-training branch (#193), which carried the full instrument panel (Models, Data, Train, Eval/Embeddings, Quantize, Runs, Adapters). Per the v1 scope, everything except Models and Chat is cut and re-addable incrementally as the backend matures.

Shipped

• MODELS (⌘1) — browse / Get Models / Refresh / Reveal-in-Finder, a single Chat CTA, and the full model-config readout inspector (format, dtype, params, hidden, FFN, vocab, ctx, heads, KV heads, head dim, GDN heads, layers, size, files, tokenizer — all honest-nil when the config lacks the field).
• CHAT (⌘2) — single-mode local generation over CPU bf16 and GPU Metal (bf16 + q4), honest disk-status (ready / not found, never "loaded"), Sampling (temp / top-k / top-p / rep-penalty) and Generation (max-tokens / seed) controls, streaming transcript with retry and tok/s + honest hardware label.

Deferred (re-addable as backend matures)

Data, Train, Eval & Embeddings, Quantize, Runs & History, adapter management.

Notes

• Screen enum reduced to {models, chat}; nav rail, ⌘K command bar, and run-status routing follow the two-screen shape.
• No adapter path is threaded through Chat generation (adapterPath: nil); no +LoRA inference tag.
• Unused store / model scaffolding (eval/train/quant state, extra domain types) is left compiling for clean incremental revival rather than deleted, keeping the diff minimal.
• No engine binaries are added — the app shells out to binaries already on main. (git diff --name-only main..HEAD -- 'crates/*/src/bin/' is empty.)

Test plan

• swift build green on a forced recompile (every edited file actually recompiled, not cached)
• No orphaned references to the removed screens (statically-typed build is dispositive)
• Commit pre-commit hook passed (cargo check workspace + doc lint)
• Visual click-through on a Finder-launched .app (Ocean)

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