docs(changelog): add Fixed entries for PRs #1498, #1481, #1479

- tool add: handle tool: wrapper key (#1471)
- session export: sha256: prefix checksum (#1450)
- ThoughtBlockWidget: correct background color (#1448)

ISSUES CLOSED: #1471 #1450 #1448

CHANGELOG.md

@@ -32,6 +32,18 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   the "persists across restarts" requirement. 47 new BDD scenarios cover typed
   triples, temporal queries, and provenance. (#891)
 
+### Fixed
+
+- `agents tool add` now accepts YAML configs using the spec-required `tool:` wrapper key
+  (e.g. `tool:\n  name: ...`). The `cleveragents:` version header is silently ignored.
+  Flat format (without wrapper) remains supported for backward compatibility. (#1471)
+
+- Session export checksum format corrected from raw hex to `sha256:`-prefixed format as
+  required by the specification. (#1450)
+
+- `ThoughtBlockWidget` background corrected from `$primary 20%` to `$primary-muted 20%`,
+  making thought blocks visually lighter and more subtle per spec §29811. (#1448)
+
 ## [3.7.0] — 2026-04-02
 
 ### Added