docs: retire the stray top-level web-ui.md, fold it into web-ui/README.md

docs/web-ui.md duplicated the web-ui/ directory name at the top level --
the only such collision in docs/ (every other subsystem has just a
directory, no sibling <dir>.md file). That's exactly why it rendered
outside the directory structure in the docs site nav (mara's report,
hyperhive#4054): the site build walks docs/ generically with no
special-casing, so a loose top-level file next to a same-named
directory shows up as its own flat top-level entry instead of nesting
under that directory's section.

web-ui.md's own first paragraph already said as much -- 'This doc has
been split for readability... start at web-ui/README.md instead.' It
was a leftover pointer from before the split, not a page carrying
unique content on its own merit.

Folded its two sections web-ui/README.md didn't already have (the
swarm-ui design-guide link, and the task-oriented 'reading paths'
quick-lookup list) into web-ui/README.md's existing 'More depth'
section, then deleted the stray file and repointed every real
reference at it: 3 in-tree doc cross-links, 3 doc prose mentions
(retargeted to the more specific dashboard.md/shape.md sub-page each
one was actually about), and ~28 frontend source comments
(dashboard/agent/shared packages) that cited it as
'docs/web-ui.md::<heading>' for implementation context -- retargeted
each to whichever of dashboard.md/shape.md/agent.md actually carries
that heading now, verified against each file's real heading list
rather than guessed.

Verified via scripts/check-doc-refs.sh (the same lint CI runs): 0 dead
pointers, both before write (confirming the tree was clean beforehand)
and after (confirming nothing broke).

frontend/packages/shared/src/side-panel/hive-side-panel.js

@@ -31,7 +31,7 @@ import { el } from "../dom.js";
 import { attachShadowCss } from "../shadow-css.js";
 import sidePanelCss from "./hive-side-panel.css";
 
-// See docs/web-ui.md::Side panel for the hit-strip + pointer-capture +
+// See docs/web-ui/agent.md::Side panel for the hit-strip + pointer-capture +
 // localStorage persistence model; CSS clamps the stored value to min
 // 320px / max 96vw and out-of-range stored values are dropped silently.
 // Shared by both packages deliberately — see module header.

frontend/packages/shared/src/terminal/terminal.js

@@ -12,7 +12,7 @@ const NEAR_BOTTOM_PX = 48;
 // "load older" fetch — fires via the scroll event handler so the operator
 // never has to click the pill; the pill stays as a visual indicator.
 const LOAD_MORE_SCROLL_PX = 80;
-// Snap-to-bottom animation duration. See docs/web-ui.md::Shared
+// Snap-to-bottom animation duration. See docs/web-ui/shape.md::Shared
 // terminal pane (Sticky-bottom + snap animation) for the 140ms-vs-
 // 500ms-browser-default + 24px short-circuit rationale.
 const SCROLL_ANIM_MS = 140;
@@ -128,7 +128,7 @@ export function create(opts) {
     // immediately so the MutationObserver stops re-firing snapToBottom()
     // and the animation-guard window can expire naturally. Without this,
     // live events arriving < 220ms apart permanently block scroll-to-top
-    // and loadMore() never fires. See docs/web-ui.md::Shared terminal
+    // and loadMore() never fires. See docs/web-ui/shape.md::Shared terminal
     // pane (Mid-animation scroll-event guard).
     const inAnim = Date.now() < smoothScrollingUntil;
     const nearBottom = isNearBottom();
@@ -571,7 +571,7 @@ export function create(opts) {
 }
 
 // Build a DocumentFragment from `text`, turning bare http(s) URLs into
-// clickable links that open in a new tab. See docs/web-ui.md::Shared
+// clickable links that open in a new tab. See docs/web-ui/shape.md::Shared
 // terminal pane (linkify) for the text-node-only / no-innerHTML
 // XSS-safety + trailing-punctuation strip.
 const LINKIFY_URL_RE = /https?:\/\/[^\s<>"']+/g;