fix(host): disable topology injector to eliminate 15s startup delay

[codefromthecrypt]

What this PR does / why we need it:

The topology injector adds an EDS local_cluster to the bootstrap config for zone-aware routing. In standalone/host mode, this cluster waits for endpoint discovery that never completes, causing a 15-30 second delay before Envoy reports as ready.

This change always disables the topology injector in host infrastructure mode since zone-aware routing is only relevant in Kubernetes deployments.

lsof -ti tcp:1066,1067,8080,9901,1061,1975 | xargs -r kill -9 ; rm -rf /tmp/envoy-gateway/certs; OPENAI_BASE_URL=http://localhost:11434/v1 OPENAI_API_KEY=unused out/aigw-darwin-arm64 run --mcp-json '{
>   "mcpServers": {
>     "kiwi": {
>       "type": "http",
>       "url": "https://mcp.kiwi.com"
>     }
>   }
> }'

Envoy AI Gateway listening on http://localhost:1975 (admin http://localhost:56664) after 2.8s

Which issue(s) this PR fixes:

Fixes #7080

[arkodg]

thanks for digging into this !

[mathetake]

wow good find

[nacx]

Nice catch!

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.11%. Comparing base (b4282a6) to head (53d6ebf).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/infrastructure/host/proxy_infra.go	0.00%	5 Missing ⚠️

❌ Your patch status has failed because the patch coverage (0.00%) is below the target coverage (60.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7180      +/-   ##
==========================================
+ Coverage   71.04%   71.11%   +0.07%     
==========================================
  Files         228      228              
  Lines       40676    40678       +2     
==========================================
+ Hits        28897    28927      +30     
+ Misses      10078    10059      -19     
+ Partials     1701     1692       -9     

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[codefromthecrypt]

flakes are in k8s tests, so unrelated to this local mode