docs: choose Go templ for the operator UI RFC

## Summary

### Why?

The first operator UI is queue-scoped list, summary, history, and poll. A Node BFF and overlay repo are heavier than that surface, and they do not follow the Go library/host split already used in go-code.

### What?

Rewrites `doc/rfc/web.md` to pick `templ`+HTMX as an importable Go library (`submitqueue/web`) with OSS `service/` and go-code hosts, YARPC to gateway, zap/tally. Documents Next.js as the alternative and what that choice gives up. Indexes the new shape from `doc/rfc/index.md`.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: behinddwalls

doc/rfc/index.md

@@ -10,7 +10,7 @@ Design documents and technical proposals, grouped by scope. Shared/cross-cutting
 - [Consumer Hold](consumer-hold.md) - Fourth delivery outcome letting a controller postpone its delivery: the message becomes a partition barrier that pauses consumption for a chosen delay, redelivers in order, and does not count as a failure toward dead-lettering
 - [Change URIs](change-uri.md) - Identity of a code change: `scheme://{host[:port]}/{path}` per provider (GitHub PR, Phabricator Diff, git ref/commit) and canonical-form rules
 - [Hooks Framework](hook-framework.md) - Fire-and-forget side effects off pipeline lifecycle events: one shared `HookEvent` contract (`api/base/hook/`) published to a durable per-domain hook topic, dispatched by a per-domain stage to a pluggable hook extension (`platform/extension/hook/`) for integrations like warehouse export and code-review notifications
-- [Web/UIs Design](web.md) - Per-domain Next.js/React/Base Web BFFs (`{domain}/web`), shared Node hooks (`platform/web`), example runtimes (`service/{domain}/web`), and an external overlay host for production identity and observability
+- [Web/UI Design](web.md) - Operator UI as a Go `templ`+HTMX library (`submitqueue/web`) with example and go-code hosts; Next.js BFF documented as the alternative if the UX outgrows pages and fragments
 
 ## SubmitQueue