ci: pin default Claude review model to claude-opus-4-7

[Troublor]

Summary

• The claude-pr-review composite action's model input defaulted to the opus alias, which resolves to whatever the latest Opus model is at run time (currently Opus 4.8). Every consuming repo (mega-reth, mega-evm, mega-e2e, mega-agents, mega-devops, dist-docs, watchdog-rpc, documentation) inherits this default.
• This pins the default to claude-opus-4-7 so PR reviews run on a fixed, predictable model instead of silently shifting when the alias advances to a new Opus release.
• Callers can still override via the model input, or set it empty to fall through to the claude-code-action / CLI default.

Test plan

• Change is limited to the default: value and description of the model input in .github/actions/claude-pr-review/action.yml; the composite action logic is unchanged.
• The value is passed straight through to claude --model; claude-opus-4-7 is a valid model id (hyphenated form the CLI expects).
• Verifiable on the next PR review run: the review agent job should invoke --model claude-opus-4-7.

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This PR was generated by an automated agent.

[claude]

✅ Clean

• Summary: reviewed the one-file change in .github/actions/claude-pr-review/action.yml that pins the model input default from the moving opus alias to claude-opus-4-7 and refreshes the description.
• Correctness: claude-opus-4-7 is the valid hyphenated model id passed straight through to claude --model; override path (including passing opus to opt back into the moving alias) and empty-string fall-through are preserved.
• Design: pinning a moving alias is the right call — reviews stay reproducible when the alias advances, and the change is scoped narrowly to the default plus its description.
• Repo conventions: PR title is Conventional Commits and the branch follows the {developer}/{category}/{description} pattern from CLAUDE.md.
• No new actionable findings.
• Still open from earlier reviews: none.