feat(dev-proxy): isolate local auth cookies by target

[lyzno1]

Summary

• Add target-origin scoped local cookie rewriting to the dev proxy so auth cookies from different upstream targets do not overwrite or leak into each other.
• Override the configured CSRF request header from the active scoped CSRF cookie before forwarding upstream requests.
• Enable scoped cookie rewriting for Dify's dev proxy auth cookies and document the new configuration.

Benefits

• Prevents stale localhost auth cookies from being forwarded after switching DEV_PROXY_TARGET or DEV_PROXY_ENTERPRISE_TARGET.
• Keeps independent login sessions for each upstream target origin during local development.
• Avoids app-level dev proxy knowledge by keeping CSRF header correction inside the proxy boundary.

Verification

• pnpm --dir packages/dev-proxy test
• pnpm --dir packages/dev-proxy type-check
• pnpm --dir packages/dev-proxy build
• pnpm -C web type-check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.96%. Comparing base (b0a3399) to head (c8acabf).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #36371   +/-   ##
=======================================
  Coverage   85.96%   85.96%           
=======================================
  Files        4455     4455           
  Lines      211575   211575           
  Branches    39541    39541           
=======================================
+ Hits       181878   181880    +2     
+ Misses      26483    26481    -2     
  Partials     3214     3214           

Flag	Coverage Δ
dify-ui	94.59% <ø> (ø)
web	86.56% <ø> (+<0.01%)	⬆️

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