fix(login): replace custom SWR cache with lru-cache (#11945)

# Which Problems Are Solved

The in-memory SWR promiseCache in zitadel.ts used keys like
getBrandingSettings-${org} that had no instance identifier. In
multi-tenant mode, where a single Next.js process serves multiple
instances, an instance A's cached settings without org context
(branding, languages, settings, etc.) could be served to Instance B
request without org context. The cache now additionally is bound to 100
entries by default (configurable via maxSize in `API_CACHE_CONFIG`).
When capacity is exceeded, expired entries are swept first

It additionally replaces the hand-rolled PromiseCache (Map-based, FIFO
eviction) with lru-cache, leveraging its built-in fetchMethod for
stale-while-revalidate, request deduplication, and true LRU eviction.

# How the Problems Are Solved

Added an instanceCacheKey() helpe that prefixes every cache key with
serviceConfig.instanceHost in addition to the org context if available.

---------

Co-authored-by: Ramon <[email protected]>

pnpm-lock.yaml

@@ -256,6 +256,9 @@ importers:
       escape-html:
         specifier: ^1.0.3
         version: 1.0.3
+      lru-cache:
+        specifier: ^11.3.2
+        version: 11.3.2
       lucide-react:
         specifier: ^0.577.0
         version: 0.577.0([email protected])
@@ -9286,6 +9289,10 @@ packages:
     resolution: {integrity: sha512-aY/R+aEsRelme17KGQa/1ZSIpLpNYYrhcrepKTZgE+W3WM16YMCaPwOHLHsmopZHELU0Ojin1lPVxKR0MihncA==}
     engines: {node: 20 || >=22}
 
+  [email protected]:
+    resolution: {integrity: sha512-wgWa6FWQ3QRRJbIjbsldRJZxdxYngT/dO0I5Ynmlnin8qy7tC6xYzbcJjtN4wHLXtkbVwHzk0C+OejVw1XM+DQ==}
+    engines: {node: 20 || >=22}
+
   [email protected]:
     resolution: {integrity: sha512-KpNARQA3Iwv+jTA0utUVVbrh+Jlrr1Fv0e56GGzAFOXN7dk/FviaDW8LHmK52DlcH4WP2n6gI8vN1aesBFgo9w==}
 
@@ -21867,6 +21874,8 @@ snapshots:
 
   [email protected]: {}
 
+  [email protected]: {}
+
   [email protected]:
     dependencies:
       yallist: 3.1.1