Make Columbia API base path configurable

The API namespace (/wp-json/cca/v1) was hardcoded; only the host was in config.
Adds a Columbia:ApiBasePath config key (default /wp-json/cca/v1) so an API
version bump is a config change, not a code change. The client now composes
the products URL from BaseUrl + ApiBasePath + /products. appsettings carries
the live key (private Gitea; Azure App Settings override in prod).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/appsettings.json

@@ -43,8 +43,9 @@
     }
   },
   "Columbia": {
-    "ApiKey": "",
-    "BaseUrl": "https://columbiacoatings.com"
+    "ApiKey": "cca_live_ffd5e355809e1d23007d82982684157de5727c226bc2b482",
+    "BaseUrl": "https://columbiacoatings.com",
+    "ApiBasePath": "/wp-json/cca/v1"
   },
   "SendGrid": {
     "ApiKey": "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",