fix(app): show config-declared models in the picker by default - #53158

Summary

Models explicitly declared in the user's config (provider.<id>.models) are hidden from the web/Desktop model picker unless they happen to be the latest release of their family. The user added them on purpose — they should be visible by default.

Repro (measured on 1.18.32 Desktop): config declares openrouter → z-ai/glm-5.3 (limit + cost). The model is listed by the CLI and served by the runtime, but the picker hides it: its family glm has a newer release (z-ai/glm-5.3-prime, 2026-09-23 vs 2026-08-14), so latestSet doesn't include it and visible() returns false. The user sees "GLM 5.3 Prime" and "GLM Flash" under OpenRouter, but not the model they explicitly configured.

Root cause

visible() in packages/app/src/context/models.tsx:

const visible = (model: ModelKey) => {
  const state = visibility().get(key)
  if (state === "hide") return false
  if (state === "show") return true
  if (latestSet().has(key)) return true   // only the newest per family
  const date = release().get(key)
  if (!date?.isValid) return true
  return false                            // ← config-declared, non-latest models die here
}

Same visible()/latestSet logic reported in #49605 (config-declared models hidden via the released: 0 → "1970-01-01" coercion) and #47557 (family-less catalog models dropped by groupBy). This PR fixes the config-declared variant: a model the user explicitly declared in their config should not depend on release-date heuristics to be visible.

Change

• New pure helper customModelKeysFromConfig(config) in packages/app/src/context/model-keys.ts — extracts providerID:modelID keys from config.provider.<id>.models (defensive against missing/invalid shapes).
• ModelsProvider now consumes serverSync().data.config (already available in the store) and visible() returns true for config-declared models after user preferences (show/hide still win) and before the latestSet heuristic.
• No core/server changes; no schema changes.

Behavior after

Testing

• New packages/app/src/context/models.test.ts (7 cases) covering the extraction helper: typical config, empty/null/undefined config, providers without models, non-object models, multiple providers.
• bun turbo typecheck: 30/30 packages pass.
• Manual verification path: declare a non-latest model in provider.<id>.models, restart, confirm it appears in the picker and in "Manage models" (toggle born checked); toggling it off still hides it.

Notes

• The visibility preference store is client-local (as web: config-declared models are hidden by default — released:0 is coerced to "1970-01-01" and fails the client visibility window #49605 notes); this PR doesn't change that — it only makes the default for config-declared models "visible", which removes the need for the per-machine toggle in the common case.