docs: unify casing and replace path-as-text links across recent doc surfaces

Sweep recent (last ~5h) doc edits for two readability/uniformity issues:

- Replace 42 path-as-text links of the form '[/foo/bar](/foo/bar)' with
  descriptive labels derived from each target page's frontmatter title
  (e.g. '[Anthropic]', '[Token use and costs]', '[OpenAI-compatible
  endpoints]'). Affected files include gateway/troubleshooting,
  concepts/oauth, reference/session-management-compaction, and
  reference/transcript-hygiene.
- Sentence-case Title-Cased headings and link text in Related sections
  across codex-harness, model-providers, tools/plugin, sdk-runtime,
  sdk-setup, prompt-caching, ci, cli/config, google-meet, browser,
  rich-output-protocol, subagents, web/control-ui, while preserving
  brand and proper-noun capitalization (OpenAI, Codex, Chrome, Parallels,
  Z.AI, etc.).

docs/cli/config.md

@@ -186,7 +186,7 @@ openclaw config set secrets.providers.vaultfile \
   --strict-json
 ```
 
-## Provider Builder Flags
+## Provider builder flags
 
 Provider builder targets must use `secrets.providers.<alias>` as the path.
 
@@ -279,7 +279,7 @@ Dry-run behavior:
 - `skippedExecRefs`: number of exec refs skipped because `--allow-exec` was not set
 - `errors`: structured schema/resolvability failures when `ok=false`
 
-### JSON Output Shape
+### JSON output shape
 
 ```json5
 {