feat(desktop): dedicated Providers settings + polished Accounts/API-keys UX (#38551)

* feat(desktop): dedicated Providers settings with Accounts/API-keys subnav

Rework provider configuration in the desktop app into its own Providers
page that mirrors the first-run onboarding picker, instead of burying
provider keys in the generic Tools & Keys list.

- Add a Providers settings page (providers-settings.tsx) reusing the
  onboarding picker cards/ApiKeyForm so the two surfaces stay identical
- Add a sidebar subnav (Accounts vs API keys) backed by a deep-linkable
  `pview` URL param; nested OverlayNavItem variant for a lighter active
  state so children don't compete with the parent item
- Scope provider search to the active sub-view in its native card format
  (no more accordion fallback); collapse the API-key grid to the top
  providers behind a "Show all" toggle to cut scrolling
- Launch real in-app OAuth from settings via startManualProviderOAuth;
  fix the misleading red "reason" banner that showed during an active
  connect (neutral style, hidden during a flow, omitted for direct
  per-provider launches)
- Expand PROVIDER_GROUPS and add longest-prefix matching so providers
  like xAI/Ollama group correctly instead of landing under "Other"
- Drop redundant messaging API keys from Tools & Keys (channel_managed)

Co-authored-by: Cursor <cursoragent@cursor.com>

* feat(desktop): Cursor-style provider key list with inline inputs

Replace the card-grid API-key form on the Providers page with a
per-provider list (mirrors Cursor's API keys section):

- One row per vendor with its primary key input inline; rows with extra
  vars (base URL, region, alt tokens) expand to reveal those on focus
- Set keys show their redacted value as the placeholder; Save appears on
  edit, Remove on a set key
- Hide redundant alias key fields (e.g. ANTHROPIC_TOKEN vs
  ANTHROPIC_API_KEY) unless already set, and label set aliases by env var
  name so they're unambiguous
- Smaller mono input text + compact height

Co-authored-by: Cursor <cursoragent@cursor.com>

* style(desktop): flatten providers settings UI chrome

Tighten the providers settings surface to match the newer desktop style:
remove extra card rails/borders in API-key rows, reduce visual noise in the
providers subnav, replace bespoke link-like controls with shared text-button
variants, and improve key input readability.

* feat(desktop): rework providers settings UI

- Flatten the shared OAuth picker rows (accounts + onboarding): drop the
  rounded-2xl/border cards for flat hover-bg rows; Nous hero keeps a subtle
  tint plus an animated blue→purple arc border.
- Key fields collapse to a single input: a set key reads read-only (redacted)
  and edits in place on focus/click — no Replace/Cancel chrome. Save on type,
  Esc cancels (without closing the overlay), "Remove or esc to cancel" hint.
- Non-key overrides render boxless, content-sized (field-sizing) and
  right-anchored; advanced fields align under the primary key column.
- Add `xs` control size; size fields via padding (no fixed heights).
- Cards expand on key-input focus; chevron shows on hover/expanded; expanded
  state uses a ring + softer bg tier so hover ≠ focus.
- Relocate "Get a key" to the bottom-right of the expanded panel; drop the
  redundant provider description.
- Cmd+K: add Providers (accounts) and Provider API keys deep-links.

* fix(desktop): flatten provider fields, drop input shadows, fix Cmd+K provider rank

- KeyField: collapse to one stacked label-above-input form field (drop the
  bespoke `naked`/inline/column branches); empty advanced overrides fade until
  hover/focus/set
- styles: kill the resting + focus drop shadow on shared input chrome so form
  inputs sit flat (composer keeps its own shadow)
- Cmd+K: drop stray `providers` keyword from Skills & Tools so the Providers
  settings entry ranks first for "provider"

* fix(desktop): nous portal arc blue → orange

* fix(desktop): rank appearance above settings in Cmd+K

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Brooklyn Nicholson <brooklyn.bb.nicholson@gmail.com>

apps/desktop/src/styles.css

@@ -562,6 +562,19 @@
   animation: arc-border var(--arc-duration) linear infinite;
 }
 
+/* Flip the arc's travel direction (e.g. the Nous Portal hero row). */
+.arc-border.arc-reverse::before {
+  animation-direction: reverse;
+}
+
+/* Nous Portal hero: slower, blue → orange arc. */
+.arc-border.arc-nous,
+:root.dark .arc-border.arc-nous {
+  --arc-c1: #4f8cff;
+  --arc-c2: #ff8c42;
+  --arc-duration: 3.27s;
+}
+
 @media (prefers-reduced-motion: reduce) {
   .arc-border::before {
     animation: none;
@@ -669,11 +682,10 @@ canvas {
     var(--dt-composer-ring) calc(var(--ring-pct) * var(--composer-ring-strength)),
     var(--ring-fall)
   );
-  box-shadow: var(--shadow-composer);
+  box-shadow: none;
   transition:
     background-color 200ms ease-out,
-    border-color 200ms ease-out,
-    box-shadow 200ms ease-out;
+    border-color 200ms ease-out;
 }
 
 .desktop-input-chrome:hover {
@@ -685,7 +697,7 @@ canvas {
   --ring-pct: 45%;
   --ring-fall: transparent;
   background: var(--dt-card);
-  box-shadow: var(--shadow-composer-focus);
+  box-shadow: none;
   outline: none;
 }
 
@@ -693,13 +705,6 @@ canvas {
   border-color: var(--dt-destructive);
 }
 
-.desktop-input-chrome[aria-invalid='true']:focus {
-  box-shadow:
-    0 0 0 0.125rem color-mix(in srgb, var(--dt-destructive) 18%, transparent),
-    0 0 0 0.0625rem color-mix(in srgb, var(--dt-destructive) 34%, transparent),
-    0 0.1875rem 0.625rem color-mix(in srgb, var(--dt-destructive) 12%, transparent);
-}
-
 @layer components {
   .scrollbar-dt,
   .scrollbar-dt * {