feat: group tool calls per turn + session entity graph in chat rail

Two chat UX changes (share Chat.svelte, committed together).

Tool-call grouping (ToolCallGroup.svelte):
- Replaced the one-<details>-per-tool-call list with a single
  collapsible group per assistant turn, headed by tool count + a
  name preview and a status icon (spinning wrench in progress, check
  done, X on error).
- The group auto-collapses the instant its turn finishes streaming, so
  a completed round shows as one compact pill; historical/loaded turns
  start collapsed. The auto-collapse fires once at the streaming→done
  transition, leaving manual toggles alone afterward.

Session graph rail (SessionGraph.svelte) — replaces the old
ContextRail (fleet health / pending approvals / live events), which is
deleted:
- A force-directed graph that starts empty (animated constellation
  empty state) and grows as the conversation references entities.
  Slugs are extracted from message text and tool *arguments* only —
  never bulk result rows, so a single get_health_summary doesn't dump
  all 168 entities — then validated against the backend via fetchGraph
  (cached) with check/execution probe entities excluded. Nodes are
  colored by health; edges appear once both endpoints are present.
- Clicking a node highlights it and its neighbors and opens an inline
  detail panel below: slug/type/state, health + freshness, top
  attributes, in-graph relations (clickable to hop), and a Full detail
  button opening the entity sheet.
- The rail is resizable via a drag handle (260–620px, persisted to
  localStorage). The header's global fleet-health dots are unchanged;
  only the right-rail content was replaced.

Risk: reversible_low (UI-only). The slug extractor is scoped to
focused mentions by design; edges may be slightly incomplete since
only root-fetched entities contribute edges, which is acceptable for a
session overview.

Verification: verified in the browser preview — loading a real session
built a 4-node graph (hubris/caddy/netbird-vps/strong) with the
hubris→caddy relationship edge; clicking hubris showed
"proxmox-host · active · healthy · checked 40s ago" with attributes and
relations; dragging the handle resized 320→440px and persisted; a
34-tool historical turn renders as one collapsed pill that expands on
click. tsc clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/lib/components/ToolCallGroup.svelte

@@ -0,0 +1,79 @@
+<script lang="ts">
+  import type { ToolCallResult } from '$lib/stores/chat'
+  import WrenchIcon from '@lucide/svelte/icons/wrench'
+  import CheckIcon from '@lucide/svelte/icons/check'
+  import XIcon from '@lucide/svelte/icons/x'
+  import ChevronDownIcon from '@lucide/svelte/icons/chevron-down'
+
+  // active = this message is the one currently streaming a round of tool
+  // calls. The group starts open while active (so progress is visible live)
+  // and auto-collapses the moment that round finishes; a loaded/historical
+  // message is never active, so it starts collapsed. Once the effect below
+  // fires the one-time auto-collapse, manual toggles are left alone.
+  let { tools, active = false }: { tools: ToolCallResult[]; active?: boolean } = $props()
+
+  let open = $state(active)
+  let wasActive = active
+
+  $effect(() => {
+    if (wasActive && !active) {
+      open = false
+    }
+    wasActive = active
+  })
+
+  const doneCount = $derived(tools.filter((t) => t.type === 'tool_result').length)
+  const hasError = $derived(tools.some((t) => t.type === 'tool_result' && t.error))
+  const inProgress = $derived(active && doneCount < tools.length)
+  const names = $derived(tools.map((t) => t.name).join(', '))
+
+  function toolSummary(args: unknown): string {
+    if (!args || typeof args !== 'object') return ''
+    return Object.entries(args as Record<string, unknown>)
+      .map(([k, v]) => `${k}=${typeof v === 'string' ? v : JSON.stringify(v)}`)
+      .join(' ')
+      .slice(0, 80)
+  }
+</script>
+
+{#if tools.length}
+  <details bind:open class="group w-fit max-w-full overflow-hidden rounded-lg border bg-card text-xs">
+    <summary class="flex cursor-pointer select-none items-center gap-2 px-2.5 py-1.5 hover:bg-muted/50 [&::-webkit-details-marker]:hidden">
+      {#if inProgress}
+        <WrenchIcon class="size-3 shrink-0 animate-pulse text-primary" />
+      {:else if hasError}
+        <XIcon class="size-3 shrink-0 text-destructive" />
+      {:else}
+        <CheckIcon class="size-3 shrink-0 text-success" />
+      {/if}
+      <span class="font-medium">{tools.length} tool{tools.length === 1 ? '' : 's'}</span>
+      <span class="max-w-64 truncate font-mono text-muted-foreground">{names}</span>
+      <ChevronDownIcon class="size-3 shrink-0 text-muted-foreground transition-transform group-open:rotate-180" />
+    </summary>
+    <div class="flex flex-col divide-y border-t">
+      {#each tools as tool (tool.id)}
+        <div class="p-2">
+          <div class="flex items-center gap-2">
+            {#if tool.type === 'tool_result' && tool.error}
+              <XIcon class="size-3 shrink-0 text-destructive" />
+            {:else if tool.type === 'tool_result'}
+              <CheckIcon class="size-3 shrink-0 text-success" />
+            {:else}
+              <WrenchIcon class="size-3 shrink-0 animate-pulse text-primary" />
+            {/if}
+            <span class="font-mono font-medium">{tool.name}</span>
+            <span class="max-w-64 truncate text-muted-foreground">{toolSummary(tool.args)}</span>
+          </div>
+          <div class="mt-1 max-h-48 overflow-y-auto rounded bg-background/60 p-2">
+            {#if tool.args}
+              <pre class="whitespace-pre-wrap break-all font-mono text-[11px] text-muted-foreground">{JSON.stringify(tool.args, null, 2)}</pre>
+            {/if}
+            {#if tool.type === 'tool_result'}
+              <pre class="mt-1 whitespace-pre-wrap break-all font-mono text-[11px] {tool.error ? 'text-destructive' : ''}">{tool.error ?? JSON.stringify(tool.result, null, 2)}</pre>
+            {/if}
+          </div>
+        </div>
+      {/each}
+    </div>
+  </details>
+{/if}