ci: revert architectural-rules to composer install

[fain182]

Summary

• Reverts f37a022, which switched the self-architectural-test from composer install + bin-stub/phparkitect to downloading the released PHAR.
• That switch is incompatible with the v1.0 PHAR by design: running phparkitect as a PHAR requires --autoload, but phparkitect's own vendor/autoload.php registers Arkitect\\: src/ and shadows the PHAR's internal scoped classes — typehints resolve to the unscoped Symfony\…\OutputInterface while runtime instances are _PhpArkitect\Symfony\…\StreamOutput, and check blows up.
• See the run that surfaced this: https://github.com/phparkitect/arkitect/actions/runs/24964604016/job/73097115614
• Going via composer install runs everything in the same (unscoped) namespace, so there's no conflict — same approach we used before f37a022.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.32%. Comparing base (7b1fa40) to head (bea5347).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #614   +/-   ##
=========================================
  Coverage     98.32%   98.32%           
  Complexity      689      689           
=========================================
  Files            86       86           
  Lines          1968     1968           
=========================================
  Hits           1935     1935           
  Misses           33       33           

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