Release v0.2.8 — PHPStan CI green again

After the v0.2.6 G → RequestContext rename, PHPStan flagged 90
"unknown class" errors because it doesn't follow runtime class_alias.
This release migrates framework-internal G:: references to the
canonical RequestContext:: name across src/. The class_alias for
external user-code backward compat is unchanged.

PHPStan: 0 errors. Unit tests: 155/155.