docs(dashboard): document themed dialog system + graceful-stop checkbox

The dashboard now routes all confirms/prompts/error notices through the
in-app themed dialog system (modal.js: themedConfirm / themedPrompt /
themedToast) instead of native browser chrome, and the stop action carries
a 'stop gracefully' checkbox that POSTs /kill/<name>?graceful=1. Document
both in the web-ui reference, with the note that the backend quiesce is
still being implemented so the graceful flag currently behaves as a hard
stop.

docs/web-ui/dashboard.md

@@ -755,7 +755,8 @@ per-agent actions and navigation links. Contents:
 - `journal logs →` — opens `/logs.html#agent?agent=<name>` so the
   operator lands directly in the AGENT log tab pre-filtered to this
   container, without having to pick an agent from the dropdown.
-- `DESTR0Y` / `PURG3` — destructive, each prompts for confirmation.
+- `DESTR0Y` / `PURG3` — destructive, each prompts for confirmation
+  via the themed dialog (see **Themed dialogs** below).
 - `deployed:<sha> ↗` — present when the agent has a `deployed_sha`
   and the forge is reachable; links the deployed commit on the forge
   agent-configs mirror.
@@ -764,6 +765,41 @@ per-agent actions and navigation links. Contents:
 agent is stale. Banner pulses on each broker SSE event
 (`pulseBanner` with a 4s grace timer).
 
+### Themed dialogs
+
+All confirmations, prompts, and transient error notices use an
+in-app themed dialog system (`assets/modal.js`) rather than the
+browser's native `confirm()` / `prompt()` / `alert()` chrome, so
+they match the Catppuccin palette and can't be styled away by the
+OS. Three primitives, all built on the `openDialog` core:
+
+- `themedConfirm({ message, danger, confirmLabel, checkboxes })`
+  — a modal confirm that resolves to `null` on cancel or an object
+  of checkbox states on confirm. Destructive actions pass
+  `danger: true` (the confirm button turns red and the cancel
+  button takes focus). Backdrop click and `Esc` both cancel.
+- `themedPrompt(...)` — a modal with a text input, resolving to the
+  entered string or `null`.
+- `themedToast({ type, ... })` — a non-blocking toast (top-right,
+  `info` / `error` / `ok`) for transient validation + action
+  failures, so an error doesn't trap the operator behind a modal.
+  Single-action errors auto-dismiss; bulk / partial-failure
+  summaries are sticky (click to dismiss) so they aren't missed.
+
+Every destructive run-state action (`ST0P`, `R3ST4RT`, `R3BU1LD`,
+`DESTR0Y`, `PURG3`, `M0V3`) routes through `themedConfirm`, on both
+the per-agent `⋮` menu and the bulk selection bar.
+
+**Graceful stop** — the `■ ST0P` confirm dialog (per-agent and
+bulk) carries a `stop gracefully — let the agent finish its turn
+and flush state before the container stops` checkbox. When ticked,
+the action POSTs `/kill/<name>?graceful=1` (the bulk path appends
+the flag per-agent); unticked is today's instant hard stop
+(`/kill/<name>` with no query). NOTE: the per-agent quiesce is
+still being implemented (see the graceful-agent-stop tracker) — the
+flag is accepted now so the wire shape is stable, but the backend
+currently treats a graceful request the same as a hard stop.
+
 ### Topology tree
 
 Container rows render as a forest, not a flat list — each agent