Update Ember agent model to claude-opus-4.7

[jennyf19]

Bumps the Ember agent's default model from claude-opus-4.6 to claude-opus-4.7 so new users get the latest Claude Opus release out of the box.

Single-line frontmatter change; agent prompt is unchanged.

[github-actions]

🟡 Contributor Reputation Check: MEDIUM risk

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[github-actions]

🔒 PR Risk Scan Results

Scanned 1 changed file(s).

Severity	Count
🔴 High	0
🟠 Medium	0
ℹ️ Info	0

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[github-actions]

🔍 Vally Lint Results

⚠️ Warnings or advisories found

Scope	Checked
Skills	0
Agents	1
Total	1

Severity	Count
❌ Errors	0
⚠️ Warnings	0
ℹ️ Advisories	1

Summary

Level	Finding
ℹ️	Vally currently lints SKILL.md content. Agent files were detected but skipped:

Full linter output

### Agent files detected (not linted by vally)
ℹ️ Vally currently lints SKILL.md content. Agent files were detected but skipped:
agents/ember.agent.md

[Copilot]

Pull request overview

This PR updates the Ember agent’s frontmatter to use claude-opus-4.7 as its default model, keeping the agent prompt content unchanged while ensuring new users default to the newer Opus version.

Changes:

• Bump agents/ember.agent.md model from claude-opus-4.6 to claude-opus-4.7.