feat(views,surface-host): Extensions sidebar view — auto-expanded surfaces + tables

views (new feature):
- pure panel-stack reducer + thin generic ViewSidebar (dropdown picker + add/remove),
  switches on view KIND, never a surface id

Extensions view (composition root):
- folds frontend modules + backend surfaces into one "Extensions" view
- frontend module list AGGREGATED from each feature's public `manifest` export
  (can't drift); no per-module version (FE features are internal to dispatch-web)
- surfaces are AUTO-SUBSCRIBED on catalog + rendered expanded (no catalog buttons)

surface-host:
- consecutive `stat` fields coalesce into one aligned label/value table (StatTable)
- generic custom-field renderer: dispatch on rendererId === "table" → SurfaceTable
  (pure parseTablePayload), so a backend `custom`/table field renders generically
- shared presentational components/Table.svelte (used by both, neither feature
  depends on the other)

store:
- auto-subscribe every catalog entry, unsubscribe vanished ones, re-subscribe all
  on reconnect; expose all received specs via `surfaces` (drops single-selection)

backend-handoff: CR-1 — emit Loaded Extensions as a custom/table field; notes
what's already covered FE-side (renderer shipped, stat-table fallback works).

4 files changed, 58 insertions, 23 deletions

diff --git a/src/features/surface-host/ui/Stat.svelte b/src/features/surface-host/ui/Stat.svelte
deleted file mode 100644
index e184dab..0000000
--- a/src/features/surface-host/ui/Stat.svelte
+++ /dev/null
@@ -1,10 +0,0 @@
-<script lang="ts">
-	import type { StatFieldView } from "../logic/types";
-
-	let { field }: { field: StatFieldView } = $props();
-</script>
-
-<dl>
-	<dt>{field.label}</dt>
-	<dd>{field.value}</dd>
-</dl>
diff --git a/src/features/surface-host/ui/StatTable.svelte b/src/features/surface-host/ui/StatTable.svelte
new file mode 100644
index 0000000..415423f
--- /dev/null
+++ b/src/features/surface-host/ui/StatTable.svelte
@@ -0,0 +1,21 @@
+<script lang="ts">
+	import type { StatFieldView } from "../logic/types";
+
+	// Renders a run of stat fields as one aligned label/value table. Headerless:
+	// the column semantics aren't known generically, but the two-column layout
+	// gives the tidy, aligned readout the stats deserve (e.g. extension → version).
+	let { stats }: { readonly stats: readonly StatFieldView[] } = $props();
+</script>
+
+<div class="overflow-x-auto">
+	<table class="table table-sm">
+		<tbody>
+			{#each stats as stat, i (i)}
+				<tr>
+					<th class="font-medium">{stat.label}</th>
+					<td class="text-right tabular-nums">{stat.value}</td>
+				</tr>
+			{/each}
+		</tbody>
+	</table>
+</div>
diff --git a/src/features/surface-host/ui/SurfaceTable.svelte b/src/features/surface-host/ui/SurfaceTable.svelte
new file mode 100644
index 0000000..764cc36
--- /dev/null
+++ b/src/features/surface-host/ui/SurfaceTable.svelte
@@ -0,0 +1,14 @@
+<script lang="ts">
+	import Table from "../../../components/Table.svelte";
+	import { parseTablePayload } from "../logic/table";
+
+	let { payload }: { readonly payload: unknown } = $props();
+
+	// Parse defensively; an unparseable payload yields null → render nothing
+	// (graceful skip, per the custom-field contract).
+	const data = $derived(parseTablePayload(payload));
+</script>
+
+{#if data !== null}
+	<Table columns={data.columns} rows={data.rows} />
+{/if}
diff --git a/src/features/surface-host/ui/SurfaceView.svelte b/src/features/surface-host/ui/SurfaceView.svelte
index 4207913..5210e8c 100644
--- a/src/features/surface-host/ui/SurfaceView.svelte
+++ b/src/features/surface-host/ui/SurfaceView.svelte
@@ -1,10 +1,11 @@
 <script lang="ts">
 	import type { InvokeMessage, SurfaceSpec } from "@dispatch/ui-contract";
-	import { planSurface } from "../logic/plan";
+	import { groupRenderFields, planSurface } from "../logic/plan";
 	import Button from "./Button.svelte";
 	import Progress from "./Progress.svelte";
 	import Selector from "./Selector.svelte";
-	import Stat from "./Stat.svelte";
+	import StatTable from "./StatTable.svelte";
+	import SurfaceTable from "./SurfaceTable.svelte";
 	import Toggle from "./Toggle.svelte";
 
 	let {
@@ -13,21 +14,30 @@
 	}: { spec: SurfaceSpec; onInvoke: (msg: InvokeMessage) => void } = $props();
 
 	const plan = $derived(planSurface(spec));
+	// Consecutive stats render together as one aligned table; everything else is
+	// a standalone widget. Grouping keys on field KIND only — never the surface id.
+	const groups = $derived(groupRenderFields(plan.fields));
 </script>
 
 <article>
 	<h2>{spec.title}</h2>
-	{#each plan.fields as field (field)}
-		{#if field.kind === "toggle"}
-			<Toggle {field} surfaceId={spec.id} {onInvoke} />
-		{:else if field.kind === "progress"}
-			<Progress {field} />
-		{:else if field.kind === "selector"}
-			<Selector {field} surfaceId={spec.id} {onInvoke} />
-		{:else if field.kind === "stat"}
-			<Stat {field} />
-		{:else if field.kind === "button"}
-			<Button {field} surfaceId={spec.id} {onInvoke} />
+	{#each groups as group, i (i)}
+		{#if group.type === "stats"}
+			<StatTable stats={group.stats} />
+		{:else if group.field.kind === "toggle"}
+			<Toggle field={group.field} surfaceId={spec.id} {onInvoke} />
+		{:else if group.field.kind === "progress"}
+			<Progress field={group.field} />
+		{:else if group.field.kind === "selector"}
+			<Selector field={group.field} surfaceId={spec.id} {onInvoke} />
+		{:else if group.field.kind === "button"}
+			<Button field={group.field} surfaceId={spec.id} {onInvoke} />
+		{:else if group.field.kind === "custom"}
+			<!-- Dispatch on rendererId (a renderer KIND, never a surface id);
+			     unknown ids gracefully render nothing. -->
+			{#if group.field.rendererId === "table"}
+				<SurfaceTable payload={group.field.payload} />
+			{/if}
 		{/if}
 	{/each}
 </article>