feat(desktop): long-press a rail profile to pick its color

Hold (~450ms) a profile square — or right-click → Color… — to open a
shadcn Popover of swatches and override its rail color, with Auto to fall
back to the deterministic hue. The hold timer rides alongside the dnd
pointer listener (a real drag cancels it, the trailing click is
suppressed), so reorder/select/recolor stay distinct gestures.

Overrides persist in localStorage ($profileColors), resolved via
resolveProfileColor (override wins, else the name-hashed hue). Cosmetic
and gated on the multi-profile rail, so single-profile users are
unaffected. Adds a reusable ui/popover.tsx (radix-ui umbrella).

apps/desktop/src/store/profile.ts

@@ -3,7 +3,15 @@ import { atom, computed } from 'nanostores'
 import { getProfiles, setApiRequestProfile } from '@/hermes'
 import { resolveGatewayWsUrl } from '@/lib/gateway-ws-url'
 import { queryClient } from '@/lib/query-client'
-import { arraysEqual, persistBoolean, persistStringArray, storedBoolean, storedStringArray } from '@/lib/storage'
+import {
+  arraysEqual,
+  persistBoolean,
+  persistStringArray,
+  persistStringRecord,
+  storedBoolean,
+  storedStringArray,
+  storedStringRecord
+} from '@/lib/storage'
 import { $gateway } from '@/store/gateway'
 import { setConnection } from '@/store/session'
 import type { ProfileInfo } from '@/types/hermes'
@@ -62,6 +70,30 @@ export function sortByProfileOrder<T extends { name: string }>(items: T[], order
   })
 }
 
+// ── Rail colors ────────────────────────────────────────────────────────────
+// Optional per-profile color override (long-press a rail square to pick). Absent
+// names fall back to the deterministic hue from profileColor(); a local-only
+// cosmetic preference, so single-profile users never touch it.
+const PROFILE_COLORS_STORAGE_KEY = 'hermes.desktop.profileColors'
+
+export const $profileColors = atom<Record<string, string>>(storedStringRecord(PROFILE_COLORS_STORAGE_KEY))
+
+$profileColors.subscribe(value => persistStringRecord(PROFILE_COLORS_STORAGE_KEY, value))
+
+// Set (or, with null, clear) a profile's color override.
+export function setProfileColor(name: string, color: null | string): void {
+  const key = normalizeProfileKey(name)
+  const next = { ...$profileColors.get() }
+
+  if (color) {
+    next[key] = color
+  } else {
+    delete next[key]
+  }
+
+  $profileColors.set(next)
+}
+
 interface ActiveProfileResponse {
   active: string
   current: string