tabs.js + web-ui.md: drop 'no special-case manager' framing (mara on #728)

mara's review nit: explaining the absence of a manager special-case
implicitly endorses the idea that special cases would be normal.
Default is no special case; the doc shouldn't dwell on it.

- ST0P comment block removed entirely (the bulk-button line above
  is self-explanatory; the substantive 'c0re survives manager-down'
  rationale lives in the host docs, not here).
- M0V3 helper comment reframed: trim the 'no special-case' framing
  but keep the substantive note that the backend refuses moves it
  can't satisfy and the failure surfaces in the bulk roll-up.
- docs/web-ui.md::Selection bar bullet list: drop the 'manager
  included; no special-case' qualifiers; just describe the action.
  M0V3→ROOT keeps the rationale that backend refusals surface in
  the roll-up but stops calling out manager specifically.

docs/web-ui.md

@@ -522,15 +522,15 @@ frosted-mauve bar slides up from the bottom of the viewport
   support the action; disabled with a tooltip naming the blockers
   when the selection is mixed:
   - `↺ R3ST4RT` — running agents only
-  - `■ ST0P` — running agents only (manager included; no special-case)
+  - `■ ST0P` — running agents only
   - `▶ ST4RT` — stopped agents only
   - `↻ R3BU1LD` — always available
   - `DESTR0Y` / `PURG3` — sub-agents only (disabled if manager selected)
   - `⇡ M0V3 → ROOT` (#486) — promote selected agents to top-level
     (parent = null); disabled when all selected are already at root.
-    Manager included with no special-case (matches the `ST0P` policy);
-    the backend's `topology::set_parent` refuses to move the manager
-    and the refusal surfaces in the failure roll-up.
+    Backend `topology::set_parent` refuses moves it can't satisfy
+    (e.g. moving the manager) and the refusal surfaces in the
+    failure roll-up.
   - `⇢ M0V3 → [select]` (#486) — inline picker available for any
     selection size. The dropdown lists every container that isn't IN
     the selection itself nor a descendant of any selected agent