Add tests for process-environment.sh and fix POSIX compliance

[kmcginnes]

Description

Add a comprehensive test suite for process-environment.sh and fix POSIX shell compliance issues.

• Add 26 tests covering SSL defaults, Neptune notebook overrides, config.json priority, defaultConnection.json generation, SERVICE_TYPE auto-detection, custom config paths, and file behavior
• Replace echo -e with printf for POSIX compliance since echo -e is a bashism
• Replace == with = in test expressions since == is not POSIX sh
• Tests now run under sh to match the script shebang

Validation

• All 26 tests pass under sh
• pnpm checks passes (lint, format, types)
• pnpm test passes for the new test file

Related Issues

• Part of Improve proxy server testability #1633

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.20%. Comparing base (c5affc5) to head (20de3b6).
⚠️ Report is 113 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1629       +/-   ##
===========================================
+ Coverage   47.81%   62.20%   +14.39%     
===========================================
  Files         382      389        +7     
  Lines        8525     8952      +427     
  Branches     3159     3430      +271     
===========================================
+ Hits         4076     5569     +1493     
+ Misses       3070     2338      -732     
+ Partials     1379     1045      -334     

Flag	Coverage Δ
unittests	62.20% <ø> (+14.39%)	⬆️

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