test(ssh): improve SSH proxy test coverage

[fabiovincenzi]

Description

Add tests to improve SSH proxy coverage, focusing on the four modules with the most gaps:

• server.ts: push flow (no-op detection, security chain integration, pack size/chunk limits, timeout), path validation, auth edge cases, debug mode
• GitProtocol.ts: happy paths for all 4 exported functions
• sshInternals.ts: all exported functions with failure modes and error messages
• AgentForwarding.ts : CHANNEL_OPEN_CONFIRMATION handler, lock recovery

Related Issue

Resolves #1586

Checklist

General

• I have read the CONTRIBUTING.md guidelines
• Commit messages follow Conventional Commits format
• I have a FINOS CLA on file

Documentation

• Documentation has been added/updated for any new features (N/A — test-only changes)

Configuration

• If configuration schema (config.schema.json) was modified (N/A — no config changes)

Tests

• Tests have been added/updated for new functionality
• Unit tests pass (npm test)
• Linting and formatting pass (npm run lint and npm run format:check)
• Type checks pass (npm run check-types)

[netlify]

✅ Deploy Preview for endearing-brigadeiros-63f9d0 canceled.

Name	Link
🔨 Latest commit	56a829d
🔍 Latest deploy log	https://app.netlify.com/projects/endearing-brigadeiros-63f9d0/deploys/6a477e19f8514c00081ec5fe

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.30%. Comparing base (3186da2) to head (56a829d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1628      +/-   ##
==========================================
+ Coverage   85.87%   90.30%   +4.42%     
==========================================
  Files          84       84              
  Lines        8109     8109              
  Branches     1376     1466      +90     
==========================================
+ Hits         6964     7323     +359     
+ Misses       1117      757     -360     
- Partials       28       29       +1     

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