add changelog to release notes

Author: louiswesterheide

docs/release-notes/corporate-memory-26-1/index.md

@@ -225,6 +225,13 @@ We are pleased to announce the release of Explore v26.1, which introduces badges
 
 We are excited to announce the release of cmemc v26.1, which expands access-condition administration, adds richer project and query catalog operations, and improves list and output consistency across the CLI.
 
+**v26.1.2 of cmemc ships the following features:**
+
+- Support for arbitrary custom HTTP request headers via `CMEMC_CUSTOM_HEADER_*` environment variables and config keys (CMEM-7546)
+    - Header name is derived from the suffix by replacing underscores with hyphens (e.g. `CMEMC_CUSTOM_HEADER_CF_ACCESS_CLIENT_ID` → `CF-ACCESS-CLIENT-ID`)
+    - Protected headers (`Authorization`, `User-Agent`) cannot be overridden and raise a configuration error
+    - Custom headers are cleared when switching connections
+
 **v26.1.1 of cmemc ships the following fixes:**
 
 - `workflow status` command