Add robotframework-falsegreen to tools list

[vinicq]

Adds one entry to src/content/resources/tools.mjs for robotframework-falsegreen, a static-analysis tool in the Robot Framework ecosystem.

It scans Robot Framework suites for tests that pass green without actually protecting anything: tests with no verification keyword, swallowed failures, and always-true checks. The scan is deterministic and uses the official robot.api. Placed next to the Robocop linter entry, since both are static-analysis tools (tags: ['']).

• Repo: https://github.com/vinicq/robotframework-falsegreen
• PyPI: https://pypi.org/project/robotframework-falsegreen/ (pip install robotframework-falsegreen, CLI rffalsegreen)
• Docs: https://vinicq.github.io/falsegreen-docs/

Source-only change as requested in the README; the build is automatic. Description is 177 characters (under the 200 limit).

[vinicq]

Gentle nudge on this one, and happy to be told it is not wanted.

Still current and still small: one file, src/content/resources/tools.mjs, six added lines, no deletions, and it merges cleanly as of today. The tool it points at is maintained and released (robotframework-falsegreen, MIT, on PyPI, CI green on main).

For precedent, #347 added a library to the same list in the same shape and was merged without trouble, so I do not think this needs anything unusual from a reviewer.

If the resources list is not taking additions right now, or if you would rather it live somewhere else, say so and I will close this myself rather than leave it sitting in the queue. @samipe, you merged the analogous one, so you are probably the right person to point at it, and apologies if you are not.