Add session learnings capture agent

[sudhirp25]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, workflow, or canvas extension file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, workflow, or canvas extension with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the main branch for this pull request.

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Description

Adds a custom agent that captures the investigative trail of a debugging or
requirement-analysis session (root cause, code artifacts touched, fix, and
reusable learnings) into a structured markdown file. Works across any
language/stack in the codebase (JS, TS, Angular, CSS, SQL, C#, Java, etc.),
not tied to a specific layer. Cross-links related past sessions via a
running INDEX.md so session notes form a searchable knowledge base over time.
Trigger: only activates when explicitly invoked (e.g. "capture this session"),
not proactively.

Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• New canvas extension.
• Update to existing instruction, prompt, agent, plugin, skill, workflow, or canvas extension.
• Other (please specify):

[github-actions]

🔒 PR Risk Scan Results

Scanned 1 changed file(s).

Severity	Count
🔴 High	0
🟠 Medium	0
ℹ️ Info	0

✅ No matching risk patterns were detected in changed files.

This is an automated soft-gate report. Findings indicate review targets and do not block merge by themselves.

[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/session-learnings-capture.agent.md