docs: Add URL redirects for restructured pages

why: Old URLs should still work after the restructuring.
what:
- Populate docs/redirects.txt with old-to-new URL mappings
- Fix changelog include path (../../CHANGES after move to reference/)
- Add title to changelog.md for toctree rendering
- Remove intermediate index files (guides/, reference/) — main index
  links to leaves directly

Author: tony

docs/guides/index.md

@@ -2,10 +2,12 @@
 (changelog)=
 (history)=
 
+# Changelog
+
 ```{currentmodule} libtmux_mcp
 
 ```
 
-```{include} ../CHANGES
+```{include} ../../CHANGES
 :parser: markdown
 ```

docs/history.md

@@ -0,0 +1,10 @@
+"about" "concepts"
+"topics/safety" "safety"
+"developing" "development"
+"api/index" "reference/api/index"
+"api/server" "reference/api/server"
+"api/tools" "reference/api/tools"
+"api/models" "reference/api/models"
+"api/middleware" "reference/api/middleware"
+"api/resources" "reference/api/resources"
+"api/utils" "reference/api/utils"