docs: QUICK-REFERENCE "Pages 404?" snippet recommends the wrong permissions

[mmcky]

Surfaced by the v0.8.0 validation study.

Problem

The "Pages 404?" troubleshooting snippet in docs/QUICK-REFERENCE.md (~line 312) recommends:

permissions:
  contents: write

That is the wrong permission for native GitHub Pages deployment and won't fix a 404. The correct permissions — stated correctly elsewhere in the same doc (~lines 90-93 and 243-245) — are:

permissions:
  pages: write
  id-token: write

Cache-key doc drift (same pass)

The cache-key documentation is also inconsistent with the code: docs/MIGRATION-GUIDE.md:244 describes build-{env-hash}-{run-id}, while setup-environment actually computes conda-{os}-{env-name}-py{ver}-{hash}-{cache-version} (setup-environment/action.yml:128). Reconcile the docs with the real keys.

Suggested fix

• Fix the "Pages 404?" snippet to pages: write + id-token: write.
• Reconcile the cache-key descriptions with the actual computed keys.

Context: QuantEcon/lectures#11.