docs/labels-and-capabilities.md: family:* section incomplete, self-contradicting statement

[rbowen]

What should happen

1. Expand the family:* label section to cover all 10 families (currently only 4 are documented).
2. Fix the "gmail is the only multi-capability tool" assertion — the table in the same doc contradicts it.

Why

The labels doc is the reference for contributors tagging PRs and issues. Incomplete family coverage means new contributors can't find the right label. The self-contradiction undermines credibility.

Which layer

Documentation (docs/, README.md, CONTRIBUTING.md)