docs: reorganize backlog with all done items under Completed section

- Move all completed items (Power Control, Console Link, Manual Refresh, Custom Poll Interval, Group by Node, Uptime Duration) under Completed
- Remove "Status: done" lines from individual items
- Keep only Search/Filter under Quick Wins

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backlog.md

@@ -6,32 +6,26 @@
 - Start/stop/restart buttons per row on VMs and LXCs.
 - Power action uses `/api2/extjs` endpoint with empty body `{}`.
 - Instant UI refresh via direct state sync + rAF flush for status messages.
-- **Status: done (merged to main)**
 
 ### Console Link
 - Console button per row opens Proxmox web UI console in new tab.
 - URL format: `/?console=lxc|qemu&vmid={id}&node={node}&resize=scale&xtermjs=1`
 - Browser session cookies handle Proxmox auth automatically in new tab.
-- **Status: done (merged to main)**
 
 ### Manual Refresh
-- Button in dashboard header that calls `mutate()` on all SWR caches
-- **Status: done (merged to main)**
+- Button in dashboard header that calls `mutate()` on all SWR caches.
 
 ### Custom Poll Interval
 - Number input in header (milliseconds) that updates polling in real-time.
 - Replaced SWR polling with a manual `setInterval` effect.
-- **Status: done (merged to main)**
-
-## Quick Wins (low effort, high value)
 
 ### Group by Node
 - Collapse/expand VMs/LXCs by node with toggle. Each node is a collapsible card with running/stopped subtotals.
-- **Status: done (merged to main)**
 
 ### Uptime Duration
 - `formatUptime()` now formats to "3d 4h 12m" (days, hours, minutes). Falls back to "4h 12m" or "12m" when days aren't needed.
-- **Status: done (merged to main)**
+
+## Quick Wins (low effort, high value)
 
 ### Search / Filter
 - Client-side text input filtering table rows by name/node/status