fix: separate WebApp analytics from console page tracking

[iamjoel]

Summary

• Route analytics by Next.js layout group so /agents captures UTM registration and app-creation attribution without conflicting with published WebApp routes.
• Add a consent-gated WebApp Amplitude instance that disables automatic tracking, page views, remote configuration, and session replay while preserving explicit webapp_run events.
• Keep Google Analytics exclusive to console routes and add regression coverage for analytics boundaries, consent changes, and WebApp event entry points.

Fixes DIFY-2948

Checklist

• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.

[codecov]

Codecov Report

❌ Patch coverage is 85.52632% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.67%. Comparing base (1299d99) to head (8fc161d).

Files with missing lines	Patch %	Lines
...eb/app/components/base/amplitude/web-app-client.ts	71.79%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #41251      +/-   ##
==========================================
- Coverage   86.73%   86.67%   -0.06%     
==========================================
  Files        5429     5275     -154     
  Lines      307710   302725    -4985     
  Branches    61800    60616    -1184     
==========================================
- Hits       266886   262390    -4496     
+ Misses      35567    35106     -461     
+ Partials     5257     5229      -28     

Flag	Coverage Δ
cli	?
dify-ui	93.75% <ø> (ø)
web	86.78% <85.52%> (+<0.01%)	⬆️

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