Add tags to servers, with a tag filter on the Servers page

Servers can be tagged (prod, media, rack-1, ...) for grouping. Operators
and admins edit tags inline on a server's detail page; the input suggests
tags already used on other servers so the same word ends up spelled the
same way everywhere. Tags show as chips that keep one colour per tag, on
the server cards, in the Manage table (and its CSV export), and on the
detail page, where each chip links to the Servers list filtered by that
tag. The Servers page has a tag bar with counts; picking several tags
narrows to servers that have all of them. The filter lives in the URL, so
it survives a refresh and can be linked to. Tags are also matched by the
global search.

Tags are normalized on the server (trimmed, lowercased, spaces become "-",
duplicates merged, sorted); letters in any language are allowed, plus
digits and - _ . : /, at most 30 characters and 12 per server. Invalid
input is rejected with a message naming the offending tag, and nothing is
saved. Changes are audit-logged with the before and after lists.

Stored as a JSON column on servers (migration 0010). Every server response
now returns tags as an array, and the shared response shaping strips the
token hash in one place instead of five.

Verified with 27 backend checks (normalization edge cases including
Swedish letters, roles, validation, search, audit, PATCH/detail/list
shapes) and by driving the real Servers and detail pages against the real
router in a browser (filtering, editing, invalid tag, viewer view). Real
dev database mtime untouched.

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

README.md

@@ -142,6 +142,12 @@ raise one notification when the problem starts and one when it clears (both
 thresholds are set under Settings → Notifications). Active problems are
 remembered across restarts, so a rebuild doesn't re-alert them.
 
+**Tags** — servers can be tagged (prod, media, rack-1, …) from their detail
+page by operators and admins. Tags show as coloured chips on the Servers page,
+which can be filtered by one or several tags (the filter is in the URL, so a
+tag on a server's page links to everything sharing it), and they're searchable
+from the global search box.
+
 **Maintenance mode** silences alerts about one server, integration, or DNS
 provider while you work on it (server offline / disk, storage and Synology
 health, Proxmox backup alerts, and "integration down" for that service type).