Make every table sortable and exportable to CSV

Applies the useSortable/SortableTh infrastructure introduced in the
Diagnostic Log commit to the rest of the app's tables: Audit Log,
Users, Servers (manage table), server task tables (grouped by
schedule type, on both the all-servers and per-server views), DNS
providers/zones/records, Docker containers, Gitea repos, Integrations
(manage table), IP Addresses, Proxmox guests, Secrets (already had
CSV, gained sorting), Semaphore templates, Synology volumes/disks, and
Tailscale devices.

Every column header is now click-to-sort (again on the raw field, not
its formatted display -- a byte count sorts numerically even though
the cell shows "1.2 GB", a date sorts chronologically even though the
cell shows "5d 15h 2m"), and every table got an "Export CSV" button
next to its Refresh button, exporting whatever's currently
sorted/filtered via the existing downloadCsv util.

Grouped tables (ServerTaskTable renders one sub-table per schedule
type) can't call the useSortable hook per group without breaking the
Rules of Hooks, so extracted its comparison core as a standalone
sortItems() function, driven by one shared sort-state pair at the
component's top level and applied per group.

Deliberately left two small (1-6 row) tables embedded inside stat
cards unsorted -- Proxmox's per-node storage list and ServerDetail's
agent-reported disk list -- since they're secondary detail inside an
already-scannable card, not primary list content; happy to add if
useful in practice.

Verified the shared sort core (sortItems) directly: numeric-aware
string compare (so "item2" sorts before "item10"), numbers, booleans,
and that null/undefined always sort to the end regardless of
direction.

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

README.md

@@ -70,6 +70,10 @@ All modules from the original plan are built:
 
   Add/edit/enable/disable/remove each integration's credential itself
   under Integrations → Manage integrations.
+- Every table in the app is click-to-sort on any column (numbers, booleans,
+  and dates/text sort correctly regardless of how the column formats them)
+  and has an "Export CSV" button next to it that exports whatever's
+  currently sorted/filtered.
 - **Settings** (admin-only) — notification channels (Gotify, ntfy, SMTP,
   generic webhook) with per-channel test buttons, per-event toggles (DNS
   record added/updated/deleted, daily secret-expiry reminder and daily