ci: add automated Claude PR review workflow

[dangrondahl]

Closes #32. Modelled on terraform-provider-kosli's claude-review.yaml, adapted to this repo.

Three jobs, split by PR author

Job	Fires on	Budget
review-dependency-updates	dependabot[bot]	$3
review-catalog-update	github-actions[bot] on chore/update-catalog	$3
review-general	everyone else	$5

Classification uses pull_request.user.login rather than github.actor, so a job doesn't change identity when a human pushes to a bot's branch.

The catalog job

This one has no counterpart upstream, and it is the reason a third job exists. The reference's dependency prompt is about changelogs and semver, which says nothing useful about a regenerated catalog.

Instead it summarises added, removed, and changed actions, and insists that removals be confirmed against the live spec before merge. That case has come up twice: #16 was a stale branch clobbering the catalog, #18 was a genuine upstream retirement of list_artifact_approvals. The diff alone cannot tell those apart. It also greps src/, test/, and README.md for now-dangling references, and flags any $ref that survived into the catalog.

General job

The prompt checks the deliberate design decisions recorded in CLAUDE.md: three generic tools and no tool per endpoint, generated catalog, the non-throwing { error: true, ... } contract, compact JSON.stringify, the org fallback, the User-Agent header, ESM .js import extensions, strict: true, no HTTP client library, and the readOnlyHint / destructiveHint split.

Security and conventions

• Fork PRs are skipped in all three jobs. They run without the OIDC credentials this needs, and on a public repo an unguarded trigger would let anyone spend budget.
• OIDC federation via org-wide vars, no API key secret. This is also what makes the bot paths work: Dependabot-triggered runs cannot read Actions secrets. Confirmed working on a Dependabot PR in terraform-provider-kosli (PR 232), which is itself a public repo.
• SHA-pinned actions with version comments, and harden-runner first in every job, matching the other three workflows.
• Only github.repository and the PR number are interpolated, and only into prompt: — never into a run: step.

Before merging

• Model is claude-opus-5, not the reference's claude-opus-4-8. If the federation rule doesn't permit it the first run fails loudly; switch to claude-opus-4-8, which is proven in the provider repo.
• actions/checkout is pinned to v6.0.2 to match the rest of the repo. ci: bump actions/checkout from 6.0.2 to 7.0.1 #30 bumps it to v7.0.1 — after this merges, rebase ci: bump actions/checkout from 6.0.2 to 7.0.1 #30 and it will update all four workflows together.
• Worth confirming mcp-server is in scope for the ANTHROPIC_* org variables. Reading that config needs admin:org, so I couldn't check.