fix: Legacy app detection via referer header in SSR

[thostetler]

Legacy app detection middleware wasn't working because session changes in middleware weren't visible to GSSP

• Check referer header directly in SSR instead of relying on middleware session flag
• Remove middleware and session flag overhead
• Consolidate logic into shared utility function

-- Basically it didn't work inside the middleware, since the session isn't initialized until downstream, so I moved it to ssr-utils for now

Added another commit to add back in the TRACING_HEADERS and to slightly improve the logging in the middleware

[codecov]

Codecov Report

❌ Patch coverage is 89.01961% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.4%. Comparing base (950ee95) to head (8ed72b4).

Files with missing lines	Patch %	Lines
src/utils/logging.ts	63.3%	18 Missing ⚠️
src/middleware.ts	93.4%	10 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #744     +/-   ##
========================================
+ Coverage    72.3%   72.4%   +0.1%     
========================================
  Files         221     222      +1     
  Lines       24801   24928    +127     
  Branches     1463    1477     +14     
========================================
+ Hits        17929   18028     +99     
- Misses       6831    6859     +28     
  Partials       41      41             

Files with missing lines	Coverage Δ
src/middlewares/initSession.ts	91.4% <100.0%> (+0.8%)	⬆️
src/ssr-utils.ts	68.1% <100.0%> (+0.3%)	⬆️
src/utils/legacyAppDetection.ts	100.0% <100.0%> (ø)
src/middleware.ts	93.9% <93.4%> (-0.8%)	⬇️
src/utils/logging.ts	63.3% <63.3%> (ø)

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