Thread ProviderModelSelector's loading gate to the remaining provider pickers

[atomantic]

Problem

ProviderModelSelector now takes a loading prop that disables its selects and renders "Loading providers…" instead of the caller's emptyProviderOption while the provider list is in flight. Without it, an empty providers array renders a picker whose only option is "Default (active provider)" / "Inherit (…)" — indistinguishable from a broken control.

The prop is wired for the CoS Schedule tab only (card quick-pins, plus all three pickers in the task config drawer). Every other picker still shows the bare sentinel during its own fetch window.

Sites still unwired

CoS page — same providers state, same in-flight window, already available at the render site as providersLoaded:

• client/src/pages/ChiefOfStaff.jsx — TasksTab, AgentsTab, WorkflowTab receive providers but not providersLoaded.
• TasksTab → TaskAddForm (~9 providers= call sites via TaskItem/SortableTaskItem) — note TaskAddForm also clears a pinned provider whenever enabledProviders is empty, which mid-fetch it always is; the flag prevents that by construction.
• AgentsTab → RelaunchAgentModal, ResumeAgentModal (emptyProviderOption="Auto (default)").
• WorkflowTab → AppOverridePanel → AppProviderPin (already accepts loading, just needs threading).

Pickers that fetch through useProviderModels: the hook already returns a loading flag for free at ~40 call sites; only 5 consume it (LoomEpisodeFeedback, LoomSeriesPlan, LoomEditorialAutomation, FableLoom, LoomEpisodeOutlinePlanner), and all 5 reach only disabled, never the label. Pass loading={loading} instead.

Also worth doing

getApps() and getCosLearningSummary() in ChiefOfStaff.fetchData still sit in the Promise.all whose tail is getCosActionableInsights (which fans out to cos.runHealthCheck() and detectIdleLeftoverBranches() — git work across repos). apps feeds the Schedule/Tasks/Agents app pickers, so it has the same user-visible empty-control symptom. The fix is the same .then(applyX) split; reuse the sameJsonShape identity guard so the earlier commit doesn't add a re-render per poll.

Acceptance

• No provider picker in the app renders a lone emptyProviderOption while its list is still fetching.
• apps commits on its own settle, with a sameJsonShape guard.

Follow-up to the Schedule-tab fix.

[Bryandero98]

I'd like to work on this — could you assign it to me?

[Bryandero98]

Fixed and merged in #6106.