Add CI to validate filter rules with url-filter-analyzer

[fkhb90]

Right now changes to the rule files are not automatically checked. We could add a GitHub Actions workflow that lints the generated lists on every push/PR using the companion CLI url-filter-analyzer.

Goal

• On push/PR, run ufa lint (and optionally ufa stats) against the compiled Surge / Adblock outputs
• Fail the build on lint errors (duplicate / empty rules), surface warnings in the log

Notes

• url-filter-analyzer is not yet published to npm; until then the workflow can install it from git, or this issue can wait for the npm release
• Keeps the two projects in sync and gives this repo a green CI badge

Good follow-up once url-filter-analyzer v0.1.0 is published.