feat(web): open tasks/sessions as floating windows with independent live chat

Clicking a task now opens it as a wmkit floating window (like entity
windows already do) instead of navigating away from wherever you were.
Several task windows can be open and actively streaming at once, each
fully independent — no "which one's on screen" guard needed, since
each window owns its own store bundle:

- chat.ts: chatFor(sessionId)/loadSessionChat/sendSessionMessage give
  each window its own messages/streaming/connectionState, alongside
  the existing singleton path the main Chat page still uses unchanged.
- workspace.ts: same split for plan/questions/touched/health-diffs
  (workspaceFor/startSessionWorkspace), each with its own live-event
  watermark since several windows can watch the same event stream.
- activity.ts: activityLogFor(sessionId) mirrors the global derivation.

SessionGraph.svelte, OperatorQuestion.svelte, and ActivityTimeline.svelte
were converted from store-importing to prop-driven (matching the new
ChatThread.svelte, extracted from Chat.svelte's transcript/input so both
the main page and task windows share one implementation instead of
duplicating markup/styling) so each can render either the global
"current session" or a specific window's session.

Also: minimized-window taskbar chips now cap at a max width with
middle-ellipsis truncation instead of growing unbounded, and the
window header's title/action-button row is fixed to genuinely match
heights (not just share a center point) for more robust alignment.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/pages/Overview.svelte

@@ -1,7 +1,8 @@
 <script lang="ts">
   import { onMount } from 'svelte'
-  import { fetchDashboardSummary, type DashboardSummary } from '$lib/api'
-  import { sessions, loadSessions, loadSessionMessages, newChat, sendMessage } from '$lib/stores/chat'
+  import { fetchDashboardSummary, type DashboardSummary, type Session } from '$lib/api'
+  import { sessions, loadSessions, newChat, sendMessage } from '$lib/stores/chat'
+  import { openTaskWindow } from '$lib/stores/windows'
   import { liveEvents, subscribeEvents } from '$lib/stores/events'
   import { bucket, statusStyle, FILTERS, TASK_EVENTS, heading, type Bucket } from '$lib/tasks'
   import { relativeTime } from '$lib/utils'
@@ -54,9 +55,8 @@
     filter === 'all' ? $sessions : $sessions.filter((s) => bucket(s) === filter)
   )
 
-  function openTask(id: string) {
-    loadSessionMessages(id)
-    location.hash = '#/chat'
+  function openTask(s: Session) {
+    openTaskWindow(s.id, heading(s))
   }
 
   // ── New task entry ──────────────────────────────────────────────────────
@@ -233,7 +233,7 @@
                   {@const st = statusStyle(s)}
                   <tr
                     class="cursor-pointer border-b last:border-0 transition-colors hover:bg-muted/40"
-                    onclick={() => openTask(s.id)}
+                    onclick={() => openTask(s)}
                   >
                     <td class="px-4 py-2.5">
                       <span class="flex items-center gap-1.5 text-xs font-medium text-muted-foreground">