docs: add release 0.3.1 and new Epic 2 items
docs(wiki): release v0.3.0 (stages 1c and 1d), privacy and code signing page
Mark stage 1b as released in 0.2.0, detail stage 1d, describe sharded E2E
Add stages 1c and 1d, releases 0.1.0 and 0.1.1, and Epic 6
Split stage 1b chat features from stage 1c in-game features
Update wiki for new features, releases and branch protection
Add project wiki: features, installation, building, development, testing, architecture, troubleshooting, spec and dev workflow