Settings/LLM: unified panel with per-row active toggle, edit, spend

Reworks the LLM settings surface based on UX feedback. Drops the
separate "Active LLM (this session)" card — its functionality is now
inline on each saved config as a star toggle (writes the same
localStorage key the Assistant reads via @crema/llm-providers-ui's
saveSettings, so the existing assistant code picks the change up
without any plumbing).

Per-row controls now include:
- Star: make this config active for the current browser
- Switch: enable/disable server-side
- Pencil: edit (modal, not inline-expand)
- Trash: delete (with confirm)
- Spend (30d): cost + request count, sourced from
  /api/v1/ai/llm/usage/by-model and matched on (provider, model)

Other improvements:
- Add wizard moved to a Dialog modal instead of pushing the list
  around. Same form handles edit.
- Empty state: "Seed from catalog" button creates a curated starter
  set (GPT-4o mini/4o, Sonnet 4.6, Haiku 4.5, DeepSeek V4 Flash, LM
  Studio) so first-time operators don't face a blank panel.
- Catalog dropdown picks now auto-fill input/output costs as you
  switch models, so the rates always reflect the chosen model unless
  manually overridden.
- The lib's full settings card (system prompt, transport, context
  budget) is still reachable for advanced cases — collapsed into a
  <details> below the panel.

Adds llm-configs.ts: getUsageByModel + findSpend helper for the
per-row spend lookup.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/lib/arcadia/llm-configs.ts

@@ -153,3 +153,32 @@ export async function getUsageSummary(
   )
   return "data" in (res as object) ? (res as { data: LlmUsageSummary }).data : (res as LlmUsageSummary)
 }
+
+export interface UsageByModelRow {
+  provider: string
+  model: string
+  requests: number
+  total_tokens: number
+  cost_cents: number
+}
+
+export async function getUsageByModel(
+  arcadia: ArcadiaClient,
+  opts: { days?: number } = {},
+): Promise<UsageByModelRow[]> {
+  const params: Record<string, string | number | boolean | null | undefined> = {}
+  if (opts.days != null) params.days = opts.days
+  const res = await arcadia.GET<{ data: UsageByModelRow[] } | UsageByModelRow[]>(
+    "/api/v1/ai/llm/usage/by-model",
+    { params },
+  )
+  return "data" in (res as object) ? (res as { data: UsageByModelRow[] }).data : (res as UsageByModelRow[])
+}
+
+/** Find the spend row matching a given config's (provider, model). */
+export function findSpend(
+  rows: UsageByModelRow[],
+  config: Pick<LlmConfiguration, "provider" | "model">,
+): UsageByModelRow | undefined {
+  return rows.find((r) => r.provider === config.provider && r.model === config.model)
+}