The PR template doesn't ask whether a change is breaking

[armando-navarro]

Two breaking changes reached main with no breaking-change marker:

• build: require Angular 21.2 and compile with its toolchain #3763 raised the Angular minimum to 21.2.
• build: require firebase ^12.18.0 and wrap the functions it adds #3761 raised the firebase minimum to 12.18.

Neither commit has a ! after its type or a BREAKING CHANGE: footer, so nothing in the history marks them as breaking. Users have run into unlisted breaking changes before (#2310).

PULL_REQUEST_TEMPLATE.md asks for an issue number, docs, tests and a test run, but not whether the change breaks existing apps. Asking there would prompt contributors to say so, and to mark the commit.