Allow users to pass custom build tags via `wails3 build -tags gtk4`
instead of requiring Taskfile modifications. Tags are forwarded as
EXTRA_TAGS to platform Taskfiles and appended to the go build command
alongside the existing production tag.
Works for both native and Docker cross-compilation builds.
Closes#4957
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>