Prepare 7.2.0 release

Prepare 7.1.2 CI compatibility release (#401)

## Summary

- restore compatibility across FastAPI versions that do and do not
retain `_flat_dependant`
- add regression coverage for both route shapes
- replace the invalid inline Ruff formatter suppression with a valid
block suppression
- prepare the changelog and package metadata for Cadwyn 7.1.2

## Root cause

FastAPI 0.140.2 stopped retaining flattened dependency trees, and ty
0.0.64 correctly rejected Cadwyn's direct access to the now-absent
private attribute. The current `main` SHA also used a formatter
suppression that newer Ruff rejects inside an expression.

## Impact

Scheduled dependency-refresh CI can run against current FastAPI and ty
releases while Cadwyn remains compatible with its minimum supported
FastAPI version. The release metadata is ready for 7.1.2 publication
after this PR is green and merged.

## Validation

- `make check`
- Python 3.10, 3.11, 3.12, 3.13, and 3.14 test environments
- 100% combined coverage
- lint, docs, links, tutorial, and build
- focused copy-route tests against FastAPI 0.137.1

Add release skill and prepare 7.1.1

Add support for fastapi's lazy routers (#379)

Support FastAPI 0.137.1+ included-router trees, including routes added
after inclusion, for both versioned and unversioned Cadwyn routing

Bump version to 6.2.2

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Bump version to 6.2.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Add custom static asset URL support for Swagger UI and ReDoc (#361)

Allow overriding CDN URLs for docs JS, CSS, and favicon assets
via swagger_js_url, swagger_css_url, swagger_favicon_url,
redoc_js_url, and redoc_favicon_url parameters on Cadwyn.

Closes #361

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Fix compatibility with Starlette 1.0.0 and upgrade dependencies

Starlette 1.0.0 removed the deprecated TemplateResponse(name, context)
calling convention. Switch to kwargs-based call that works on both old
and new Starlette. Also remove test for JSON body without Content-Type
which is no longer supported by FastAPI 0.132.0+.

Bump version to 6.1.1.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Fix up changelog versioning