Code splitting: store slices, GenerationPanel hook, SettingsOverlay split, model_manager submodules

[thedavidweng]

Problem

Several files exceed healthy size limits: generation.ts (~400 lines), model.ts (~427 lines), SettingsOverlay.tsx (~804 lines), model_manager/mod.rs (~1,271 lines). This hurts maintainability and makes AI-assisted editing unreliable.

Scope

• Frontend: Reduce generation.ts and model.ts below 250 lines each. Extract useGenerationForm() hook. Split SettingsOverlay.tsx into section components. Decouple FormBody field props from the whole form object.
• Backend: Split model_manager/mod.rs into submodules (download.rs, delete.rs, events.rs, mirror.rs).
• Tests: Add unit tests for new modules and slices.

Acceptance criteria

• generation.ts and model.ts each under 250 lines
• SettingsOverlay.tsx split into focused section components
• model_manager/mod.rs delegates to submodules
• New unit tests cover extracted logic
• All existing tests pass, no regressions

[github-actions]

Progress update (PR #121 merged — keeping open):

Done

• model_manager/mod.rs split into submodules (download.rs, delete.rs, manifest.rs, mirror.rs, etc.)

Not done (explicitly deferred in #121)

• generation.ts (~395 lines) and model.ts (~427 lines) still exceed 250 lines
• useGenerationForm() hook not extracted
• FormBody still coupled to the whole form object