refactor: rename service references arcadia-app → arcadia-core

The Phoenix auth/identity/tenancy backend repo is being renamed
arcadia-app → arcadia-core (its primary OTP app is already arcadia_core).
Updates prose, doc paths, and git.sky-ai.com repo URLs. Deliberately
leaves the Rust crate arcadia-app-client and host arcadia-app.internal
(handled separately), and the kept namespace (issuer/release "arcadia").

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/lib/arcadia/health.ts

@@ -2,7 +2,7 @@
 //
 // Backed by /api/v1/health* (public — no auth). Each subsystem is probed
 // independently; the overall endpoint aggregates and returns 503 if any
-// subsystem is not "ok". See arcadia-app commit f427892.
+// subsystem is not "ok". See arcadia-core commit f427892.
 
 import type { ArcadiaClient } from "@crema/arcadia-core-client"
 

app/lib/arcadia/llm-configs.ts

@@ -124,7 +124,7 @@ export async function getCatalog(arcadia: ArcadiaClient): Promise<CatalogEntry[]
 /**
  * Compute cost in cents for a given input/output token count using a
  * configuration's published rates. Mirrors `LlmConfiguration.compute_cost_cents/3`
- * in arcadia-app — keep in sync.
+ * in arcadia-core — keep in sync.
  */
 export function computeCostCents(
   config: Pick<LlmConfiguration, "input_cost_per_million" | "output_cost_per_million">,

app/lib/arcadia/llm-proxy.ts

@@ -1,6 +1,6 @@
 // Arcadia LLM proxy client.
 //
-// Implements the spec in docs/LLM_PROXY_CONTRACT.md against arcadia-app's
+// Implements the spec in docs/LLM_PROXY_CONTRACT.md against arcadia-core's
 // POST /api/v1/ai/llm/chat. The lib (@crema/llm-providers-ui buildAdapter)
 // owns the streaming chat path itself; this module exposes a lightweight
 // non-streaming probe so the Settings "Test connection" button can verify