feat(desktop): provider-level toggle in model visibility dialog

[michalmielczynski]

Problem

When all models of a provider were toggled off, closing and reopening the
dialog would auto-re-enable defaults. Empty storage was treated as
"never customized", falling back to curated defaults.

Solution

• Tombstone marker (slug::) — disabling all models stores a tombstone so
  `effectiveVisibleKeys` knows this was intentional.
• Provider-level toggle switch — one click toggles ALL models for that group.
• Persistent disabled state — stays off across dialog close/open and restarts.

Files changed

File	Change
`src/store/model-visibility.ts`	`enableProvider`, `disableProvider`, `toggleProviderVisibility`
`src/components/model-visibility-dialog.tsx`	Header toggle + visibility-filtered model rows
`src/store/model-visibility.test.ts`	4 new tests (tombstone, enable/disable cycle, provider toggle, -fast families)

6/6 tests pass. Build succeeds.

[alt-glitch]

Competing fix for #43485 alongside #43496. #43496 is the focused fix (a provider:: sentinel to stop the hide-all snap-back); this PR bundles a provider-level toggle plus unrelated electron main/preload, titlebar, and thread-virtualizer changes. Marking as duplicate of the cleaner #43496 for the same root cause — maintainer can salvage the provider-toggle UX from here.

[austinpickett]

Closing as duplicate per maintainer label. Provider-level visibility toggle is already being tracked in another PR in the queue.

[tonydwb]

Code Review Summary

Verdict: Approved

Overview

Desktop feature PR adding provider-level toggle in the model visibility dialog. Allows users to hide/show all models from a given provider at the provider level rather than per-model.

Looks Good

• Clean UI feature with proper sentinel key handling
• Correctly inserts/removes emptyProviderSentinelKey when all models are hidden/restored
• Well-scoped changes (8 files)
• No security concerns or hardcoded secrets

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Reviewed by Hermes Agent