Add recovery notes and fuller context to tickets

When an alert that opened a ticket clears, the monitor now comments on the
ticket (when it cleared, how long it lasted, failed checks, a link back).
It never closes or changes a ticket's status. Failed notes retry each
cycle for 24 hours; a 401/403 from Tinker stops them until restart.

Tickets are now Markdown with a "What to check" list and, where known:
the switch port the device plugs into (kept from the last time it was
seen, so a dead host still shows it), cutsheet cables and their path,
how often the alert fired in the last 7/30 days, other open alerts on the
device, and links into Gandalf (gandalf.public_url). Titles are unchanged
so Tinker's duplicate detection still works.

network_events gains recovery_notified, added at monitor startup; rows
that cleared before the upgrade count as already notified.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

schema.sql

@@ -21,8 +21,9 @@ CREATE TABLE IF NOT EXISTS network_events (
   resolved_at         TIMESTAMP    NULL,
   consecutive_failures INT          NOT NULL DEFAULT 1,
   ticket_id           VARCHAR(20)  NULL,
+  recovery_notified   TINYINT(1)   NOT NULL DEFAULT 0, -- recovery comment posted on ticket_id
 
-  INDEX idx_active       (resolved_at),
+  INDEX idx_active      (resolved_at),
   INDEX idx_target       (target_name, target_detail),
   INDEX idx_type         (event_type),
   -- Compound index for hot upsert_event lookup: event_type+target+resolved_at