A PR into main ran every lane, and since cloud merged into main every PR
targets main, so a one-line Dart fix waited on the Windows build. Now a
PR without a ci: line runs analyze, test and web plus the lanes its files
reach. A ci: line in the description names lanes instead, or skips CI.
Lanes guarding production and the library still run when their files
change. An unknown lane name runs everything.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>