New maglevt TUI component: out-of-band VIP health monitor

A small bubbletea TUI that reads maglev.yaml (repeatable --config),
enumerates every VIP, and probes each from outside the load balancer
on a tight cadence (default 100ms, ±10% jitter). HTTP/HTTPS VIPs get
a GET against a configurable URI (default /.well-known/ipng/healthz)
with per-VIP rolling latency (p50/p95/p99/max), lifetime N/FAIL
counters, LAST status, and a response-header tally. Non-HTTP VIPs
get a TCP connect probe. A bounded error panel classifies anomalies
as timeout / http-err / net-err / spike and auto-sizes to fill the
screen.

Utility: during a failover drill (backend flap, AS drain, config
push) the tally panel shows which backend each VIP is actually
steering to, with two-colour activity highlighting over a 5s
window — white = receiving traffic, grey = drained. Paired with
the rolling OK%/latency columns it gives an at-a-glance answer to
"is the VIP healthy from the outside right now, and which backend
is it hitting", without relying on maglevd's own view of the
world.

Also bumps Makefile/go.mod to build the new binary.

go.sum

@@ -1,7 +1,21 @@
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@@ -12,6 +26,8 @@ github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ3
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@@ -38,8 +54,22 @@ github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
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@@ -54,6 +84,9 @@ github.com/prometheus/common v0.66.1 h1:h5E0h5/Y8niHc5DlaLlWLArTQI7tMrsfQjHV+d9Z
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@@ -64,6 +97,8 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
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@@ -84,8 +119,10 @@ go.yaml.in/yaml/v2 v2.4.2 h1:DzmwEr2rDGHl7lsFgAHxmNz/1NlQ7xLIrlN2h5d1eGI=
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