docs: tidy headings

doc/dev/feature-ideas.md

@@ -1,4 +1,4 @@
-# Proposals
+# Feature ideas
 
 This section contains some potential features or redesigns that can be implemented into PixivFE.
 

doc/dev/features/exponential_backoff.md

@@ -1,4 +1,4 @@
-# Exponential Backoff in PixivFE
+# Exponential backoff
 
 PixivFE implements exponential backoff as a strategy for handling API request failures and managing token usage. This document outlines the implementation details of this feature across two key components of the application.
 

doc/dev/helpful-resources.md

@@ -1,4 +1,4 @@
-# Reference Material
+# Helpful resources
 
 This section contains multiple external links to materials/resources that could help.
 

mkdocs.yml

@@ -23,7 +23,7 @@ nav:
     - "Roadmap": "dev/roadmap.md"
     - "Testing": "dev/testing.md"
     - "Features":
-      - "Exponential backoff in PixivFE": "dev/features/exponential_backoff.md"
+      - "Exponential backoff": "dev/features/exponential_backoff.md"
       - "Caching": "dev/features/caching.md"
       - "Novels": "dev/features/novels.md"
       - "Tracing flamegraph": "dev/features/tracing-flamegraph.md"