Allow building from source / clarify web UI frontend licensing

[gokselk]

The web UI frontend source isn't in the repository, so go build fails on a fresh checkout due to the //go:embed all:dist directive requiring a web/dist directory that doesn't exist.

Could this be addressed by either:

• Including the frontend source in the repo
• Adding a build tag (e.g. //go:build web) to allow building without it
• If the frontend is intentionally closed source, noting that somewhere

Also a couple of minor things:

• The changelog lists the web UI as added in v0.9, but the server side web code (server/web*.go, web/embed.go) only appeared in v0.10
• The LICENSE file has "Copyright (c) 2025 mobydeck. All rights reserved." followed by GPLv3 "All rights reserved" contradicts the GPL grant

[arthurpro]

@gokselk thanks for reaching out! ssh2incus is currently in beta. this repo contains a snapshot of the code without the web app code because it is part of another product. the web app code will not be published until another product is fully developed and released. it will take a few months.
in the meantime we can add a build tag for this code to build correctly.