docs(update): WebFetch summarization gotcha + inline pointers (v2.4.13)

[kengio]

Summary

• Adds a Known Gotcha to skills/update/SKILL.md warning that WebFetch may post-process content (paraphrase / truncate) even on raw.githubusercontent.com URLs and even with explicit "return verbatim" prompts. Recommends curl -fsSL via the Bash tool for the four raw-content paths in /update: plugin.json + settings.json JSON parsing, PLUGIN-CHANGELOG.md verbatim display, and SKILL.md self-update bootstrap.
• Adds inline ⚠️ pointers at each of the four WebFetch call sites so a reader following the steps top-to-bottom hits the warning at the relevant moment, not only at the end of the doc. Closes the coherence gap that 3-round review flagged: warning at the bottom but step prose says "use WebFetch".
• Plugin v2.4.12 → v2.4.13 (patch — docs-only, no behavior change).

Scope

• In: Known Gotcha bullet + 4 inline pointers + changelog/version bump.
• Out: Actually swapping WebFetch → curl in the step instructions. That is a behavior change and belongs in a separate PR (likely v2.5.0) with cross-shell handling (PowerShell Invoke-WebRequest -UseBasicParsing fallback, since the curl alias on PowerShell has different flag semantics).

Review

3-round parallel sub-agent review pre-PR:

• R1 (correctness): ✅ ship-able · accurate claim · symptoms list maps to real failure modes.
• R2 (consistency): ✅ ship-able · matches docs-only patch-bump precedent (v2.4.11, v2.4.12) · style and changelog format consistent.
• R3 (completeness): ✅ ship-able · no coverage gaps · forward-compat (gotcha still reads correctly after a future curl migration).
• 3/3 consensus issue: original draft had warning only at the bottom; inline pointers added in this same PR to close the gap before merge.

Test plan

• Render skills/update/SKILL.md in Obsidian/GitHub — verify the four ⚠️ inline pointers display cleanly and the Known Gotchas section reads naturally.
• Confirm plugin.json version is 2.4.13 and PLUGIN-CHANGELOG.md frontmatter latest_version matches.
• Visually verify the changelog entry sits above v2.4.12.
• No code paths changed → no functional test needed.