Support proxy_port from registry for remote servers

[rdimitrov]

Summary

The following PR:

• Add WithRegistryProxyPort option to the run config builder
• Wire it up in both CLI (configureRemoteAuth) and API paths

Fixes stacklok/toolhive-core#54

In draft until the other change on toolhive-core is merged

Type of change

• Bug fix
• New feature
• Refactoring (no behavior change)
• Dependency update
• Documentation
• Other (describe):

Test plan

• Unit tests (task test)
• E2E tests (task test-e2e)
• Linting (task lint-fix)
• Manual testing (describe below)

Changes

File	Change

Does this introduce a user-facing change?

Special notes for reviewers

[codecov]

Codecov Report

❌ Patch coverage is 42.30769% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.61%. Comparing base (c3aeb02) to head (154cbc8).

Files with missing lines	Patch %	Lines
pkg/runner/config_builder.go	0.00%	6 Missing and 1 partial ⚠️
pkg/api/v1/workload_service.go	20.00%	3 Missing and 1 partial ⚠️
pkg/authserver/server/handlers/callback.go	50.00%	1 Missing ⚠️
pkg/authz/response_filter.go	66.66%	1 Missing ⚠️
pkg/container/images/registry.go	0.00%	1 Missing ⚠️
pkg/transport/stdio.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4039      +/-   ##
==========================================
- Coverage   68.70%   68.61%   -0.09%     
==========================================
  Files         445      445              
  Lines       45374    45386      +12     
==========================================
- Hits        31173    31142      -31     
- Misses      11796    11840      +44     
+ Partials     2405     2404       -1     

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[amirejaz]

added one nit

[amirejaz]

added another comment, sorry for fragmented review

[amirejaz]

@rdimitrov Approved from my side, need to fix the linter errors.