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/reference/session-management-compaction.md

@@ -21,12 +21,12 @@ This document explains how OpenClaw manages sessions end-to-end:
 
 If you want a higher-level overview first, start with:
 
-- [/concepts/session](/concepts/session)
-- [/concepts/compaction](/concepts/compaction)
-- [/concepts/memory](/concepts/memory)
-- [/concepts/memory-search](/concepts/memory-search)
-- [/concepts/session-pruning](/concepts/session-pruning)
-- [/reference/transcript-hygiene](/reference/transcript-hygiene)
+- [Session management](/concepts/session)
+- [Compaction](/concepts/compaction)
+- [Memory overview](/concepts/memory)
+- [Memory search](/concepts/memory-search)
+- [Session pruning](/concepts/session-pruning)
+- [Transcript hygiene](/reference/transcript-hygiene)
 
 ---