Web companion channel - the gateway's `/ui` chat instrument.

Chat-first anatomy (the ChatGPT/Claude shape): the conversation is a
centered document column - user messages as compact right-aligned
pills, vis answers as flat typeset prose behind a small accent avatar,
the execution trace folded into a 'Work' disclosure, a floating
pill composer pinned to the bottom (Enter sends, Shift+Enter breaks,
auto-grows), a thin blurred sticky header, and CONTEXT - the same
ctx mirror the model reads - as a quiet right rail.

Pure Clojure SSR: hiccup renders HTML, HTMX does declarative swaps,
the live feed is the htmx SSE extension consuming
`/ui/session/:sid/stream` - a gateway SSE stream of named HTML
fragments (activity/thinking/context) rendered server-side. Every
script is VENDORED on the classpath and served from memory
(htmx 2.0.10 + its SSE extension + ui.js) - a page
never loads anything from outside vis.

This namespace is the THIRD canonical-IR walker: the TUI walks IR
into ANSI cells, Telegram walks it into its HTML subset, and
`ir->hiccup` walks the same IR into DOM (GATEWAY.md §4.1 ALWAYS IR).

AUTO-MOUNT: the extension declares a `:gateway.slot/http-routes`
contribution; the gateway pulls it whenever it builds its handler
(whiteboard pattern - no ordering requirement, see GATEWAY.md §10.1).

Auth: none on the loopback default (`gateway-auth-required?` false);
when the gate is on, POST /ui/auth exchanges the bearer token for an
HttpOnly `vis_token` cookie that EventSource carries on SSE connect.

Theme: vis-light - white surfaces, slate neutrals, one indigo accent -
CSS variables lifted 1:1 from `internal/theme.clj` light-palette.