Add typed modeling connection errors

[pierremtb]

Summary

• add stable modeling connection error codes for authentication, account access, concurrency limits, and backend disconnects
• add an explicit retryable flag and human-readable detail
• expose a backward-compatible ModelingWebSocketResponse envelope while leaving the legacy WebSocketResponse enum unchanged for downstream Rust and generated-SDK consumers
• rebase onto the automatic OpenAPI generation workflow on current main

Tests

• cargo test -p kittycad-modeling-cmds --features websocket serialize_websocket_connection_error
• CI Rust tests, lints, formatting, Wasm check, OpenAPI regeneration, and release check pass

[codecov]

Codecov Report

❌ Patch coverage is 63.07692% with 24 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@bef38e1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
modeling-cmds/src/websocket.rs	63.07%	24 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1340   +/-   ##
=======================================
  Coverage        ?   34.65%           
=======================================
  Files           ?       36           
  Lines           ?     1870           
  Branches        ?        0           
=======================================
  Hits            ?      648           
  Misses          ?     1222           
  Partials        ?        0           

Flag	Coverage Δ
unittests	34.65% <63.07%> (?)

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