Clicking an .html/.htm file now renders it instead of showing its source or
downloading it:
- Changes/Files panel: a whole HTML file opens on Preview (Raw = the editor).
- Chat file preview: a workspace page brings its relative files along.
- File Explorer: double-click / Enter opens a viewer; Download stays on its
header and right-click menu.
The page runs in the chat artifact's sandbox (iframe srcdoc, scripts, never
allow-same-origin). Its relative stylesheets (and their url()s), scripts,
images, media and icons are read by the dashboard through the existing
download routes and inlined as <style>/data: URLs (lib/htmlInline.ts: never
above the folder's root, ≤ 60 files / 30 MB) — the login cookie is
SameSite=Strict, so a frame could not fetch them itself, and no new route
serves files without it.
