chore(release): prep v0.10.0

[ParadoxInfinite]

Prep for the v0.10.0 release (the i18n + container-shell milestone).

• Version bumped to 0.10.0 (web/package.json).
• CHANGELOG: a dated 0.10.0 section (container shell, translatable UI, translation
  contribution guardrails, Code of Conduct).
• ROADMAP: moved the in-browser shell and translations from upcoming to
  Recently shipped (v0.10.0); refreshed "Up next".
• Doc-surface audit for the new features:
  • README: dropped the now-shipped "Coming" line and the "in-browser shell" entry
    from the "where Oriel loses" list; added shell + languages to Features.
  • llms.txt: added the in-browser shell and translations to Key facts.
  • SECURITY.md: named the shell as an arbitrary-command surface in the trust model
    (same auth model, not over MCP, disablable).
  • Demo comparison: flipped the "in-browser shell" row from "on the roadmap" to
    shipped and moved it out of the "where Oriel loses" group; removed the now-unused
    roadmap tag/legend and its strings.

No code changes; docs + version only. After this merges, the release is tagged
v0.10.0-rc.1 (a pre-release, so only edge-channel users get it) for soak.