fix(desktop): honor real harness readiness in provider UI

[OmGuptaIND]

Summary

• On a fresh install, Settings showed codex as Connected (green dot) and the default-model card displayed a leftover model, even though no CLI was installed or logged in. Root cause: providerHasKey() returns true for any harness-type provider (so the CLI never needs an API key), and the desktop UI was treating that as a generic is this provider ready signal.
• Introduces isProviderReady / anyProviderReady in packages/desktop/src/lib/providers.ts as the single source of truth — consults harnessStatuses[name].installed && auth.loggedIn for harness providers, hasApiKey for API providers — and routes every relevant surface through it.
• Also fixes a pre-existing latent bug in ModelPopover.groupFor: the grouping memo didn't include harnessStatuses in its deps, so a harness login completed while the popover was open wouldn't move the provider out of "Not configured".

Surfaces fixed

• Settings > AI Models ProviderRow — "Connected" badge now reflects real CLI install + login state.
• Settings > Default model card — shows an empty state (No model selected + Select model CTA) when nothing is ready, instead of a misleading default.
• Composer ModelSelector — anyReady drives the "Select a model" empty state; the pill's old hasAnyKey predicate was always true whenever harness providers existed in the defaults list.
• ModelPopover — groupFor is now pure; the popover subscribes to harnessStatuses and includes it in memo deps so groupings update live.
• HarnessProviderSwitch — items are disabled based on real readiness; tooltip differentiates "not installed" vs "not logged in". Previously it checked p.installed, a field the backend never populates — so the switch was effectively always disabled.
• ChatInput — send button disabled when no provider is ready (tooltip: "Connect a provider to send"); Enter-key path gated in handleSend to match.
• CSS — new composer__model--empty modifier keeps the empty-state pill at the same 26px height (matching the avatar-populated pill with box-sizing: border-box) and balances horizontal padding so the label doesn't jam against the left border.

Not changed (deliberately)

• providerHasKey() in packages/agent-config/src/config.ts still returns true for harness providers. That value is load-bearing for agent-runner.ts chat gating (lines 420, 929, 1062) and there are zero tests under packages/agent-config, packages/agent-server, or packages/desktop. A frontend-only fix is tightly scoped and mirrors the already-correct ModelSelector.groupFor pattern.
• The "GLM5.1 · codex" combo that some users see as the "default" on a supposedly-fresh install can't be produced by pickDefaultProvider() (falls back to anthropic/claude-sonnet-4-6). It has to come from a leftover ~/.anton/config.yaml or a prior onboarding selection. With this change that no longer misleads the UI — a stale default is never shown as "Connected".

Test plan

No automated tests exist in this monorepo; manual QA on a clean profile:

• Stash ~/.anton/config.yaml and ensure which codex is empty.
• Launch desktop. Settings > AI Models: codex row shows Connect (not "Connected"); Default-model card shows "No model selected" + Select model button.
• Composer pill shows "Select a model"; send button disabled with the correct tooltip; Enter-key does nothing.
• Install codex but don't log in → both surfaces still show Connect; switch tooltip shows "not logged in".
• Complete codex login → Settings row flips to green "Connected" without closing Settings; popover moves codex from "Not configured" to "Subscriptions" without reopen; composer pill shows the real model; send button re-enables.
• Non-harness regression: connect an OpenAI API key → row shows "Connected" as before.

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