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
Update roadmap and features for stage 1c progress; add overlay, image drop and reload notes
Mark stage 1b as released in 0.2.0, detail stage 1d, describe sharded E2E
Roadmap: custom shareable themes in Epic 2
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
Add a roadmap page with stage 1b chat extras and later epics