[python][flask] Honor defaultController option for untagged operations

[Shaun-3adesign]

Description

The defaultController additional property was parsed but had no effect for the python-flask (Connexion) server generator: the controller module for untagged operations was always named default_controller.py, regardless of the option. (Open since 2019.)

Root cause: operations without a tag are grouped under the hardcoded "default" tag, and the controller filename is derived from that tag via toApiName. this.defaultController was stored during processOpts but never consumed.

Fix: route the default tag through the configured defaultController in AbstractPythonConnexionServerCodegen.toApiName. Because both the generated controller filename and Connexion's x-openapi-router-controller routing derive from toApiName, this single change keeps the file and the runtime routing consistent.

Verification

• New unit test PythonFlaskConnexionServerCodegenTest#testDefaultController (added a minimal spec issue_1891.yaml with an untagged operation): the untagged handler lands in the configured module, the routing extension points at the same module, and default_controller.py is no longer emitted.
• Backward compatible: with the default value, output is byte-identical — regenerating all affected samples (python-flask, python-flask-connexion3, python-aiohttp, python-aiohttp-srclayout, python-blueplanet) produced no diffs.
• Verified end-to-end at runtime: generated a Connexion 3 server with a custom defaultController, started it, and confirmed Connexion imports the renamed module and routes to it successfully.

Fixes #1891

This also resolves the defaultController half of #10765. The other half of #10765 — honoring a per-operation x-openapi-router-controller for file placement (currently the handler is written into the tag-derived file rather than the referenced module) — is a larger, separate change and will be proposed in a follow-up PR.

PR checklist

• Read the contribution guidelines.
• Ran ./mvnw clean package, ./bin/generate-samples.sh (affected python configs), and ./bin/utils/export_docs_generators.sh — no sample or docs changes result from this fix.
• Filed the PR against the master branch.
• Python technical committee: @cbornet @tomplus @krjakbrjak @fa0311

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Summary by cubic

Honors the defaultController option for untagged operations in the python-flask generator so the controller file and connexion routing use the configured module instead of default_controller.py. Behavior is unchanged when using the default value.

• Bug Fixes
  • Route the "default" tag through defaultController in toApiName, aligning the generated filename and x-openapi-router-controller.
  • Added a unit test with a minimal spec to confirm the handler lands in the custom module and default_controller.py is not generated.
  • Backward compatible: default output remains identical (no sample diffs).

^{Written for commit f7c4afa. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}