fix(ci): pin .bun-version to 1.4.2 to match bun.lock's lockfileVersion 2 (#752)

CI pinned bun 1.3.14 via .bun-version, but bun.lock on main carries
lockfileVersion 2, a format 1.3.14 cannot parse ("Unknown lockfile
version"). bun install --frozen-lockfile then fails in the shared
setup-workbench action within seconds, failing every job on every PR.
Bumping .bun-version to 1.4.2 (which already produces/reads this
lockfile format) restores frozen-lockfile install.

Claude-Session: https://claude.ai/code/session_01RweuMUskU2nvcFhdckc7EG

Author: TheGreatAxios

.bun-version

@@ -1 +1 @@
-1.3.14
+1.4.2