Docs: callers track the v0 release tag

[renmengye]

Part of #494 (step 4). v0 now exists at v0.3.0.

• examples/review.yml uses advisory-review-agent.yml@v0 with reviewer_ref: v0, and its comment explains why: v0 moves only when a release is cut, never on a push to main, so the code that receives the reviewer key changes only with releases. Pinning an exact release or SHA stays documented.
• docs/install.md: both reviewer snippets and the maintenance snippet move from @main to @v0 with reviewer_ref: v0; the "pin the version" note now recommends v0 and says that an unset reviewer_ref means main.

Not in this PR: moving v0 from release.yml on each final release, and a tag ruleset on v* (both .github/settings changes for the maintainer), and switching the caller repos.

Docs-only. Built by Claude Opus 5.5; review by the advisory panel on this PR.

[github-actions]

Round 1 — reviewed head 1c8488f2 — reviewer summarizer:hermes/gpt-5.6-terra over coverage+credentials+deployment+general+lifecycle+prose.

terra
Advisory findings from outerloop — the code owner decides. Reply to disagree; the outerloop:no-review label opts this PR out.

Verdict: 1 blocking, 0 advisory.

1 finding attached to the lines below.

Merged one blocking finding: all four substantive lenses agree that the documented rolling v0 reference is not updated by release automation. Rejected findings: none; the four reports are duplicates of the same issue.