Raise script/test's per-package timeout to 90s (closes #194)

`go test -timeout` is per package, so the budget has to clear the slowest
single package: internal/handlers. Measured in a cache-defeated builder
stage on the 48-core shared build host, 2026-08-18:

  16.9s                  host load 5-20, GOMAXPROCS 48
  45.9s / 47.3s / 49.0s  three runs at deliberate host load 31-73
  30.6s / 39.7s          host load 5-20, GOMAXPROCS 6 / 4
  67.3s / 97.5s          host load 5-20, GOMAXPROCS 2 / 1
  67.3s                  GOMAXPROCS 4 at deliberate host load 52-68

The old 30s budget was breached by every loaded run and by every
GOMAXPROCS at or below 6. At GOMAXPROCS 4 it failed outright on plain
33e4fa4 with no other change ("panic: test timed out after 30s"); with
90s the same run passes at 41.816s.

90s is the org-wide backstop in REPO_POLICIES.md. It holds against these
measurements: the worst case under native parallelism is 49.0s, and the
compound GOMAXPROCS-4-under-load case at 67.3s sits at 75% of it. The
one figure above 90s is GOMAXPROCS 1, a synthetic core floor rather
than a condition CI runs under.

No test is changed, skipped, shortened or desampled.

#194

script/test

@@ -1,12 +1,34 @@
 #!/bin/sh
 # script/test: run the test suite.
+#
+# -timeout is applied by `go test` per package, not to the run as a whole, so
+# it only has to clear the slowest single package. That is internal/handlers,
+# measured in a cache-defeated builder stage on the 48-core shared build host
+# (2026-08-18); load- and host-dependent, not invariants:
+#
+#   16.9s                  host load 5-20, GOMAXPROCS 48
+#   45.9s / 47.3s / 49.0s  three runs at deliberate host load 31-73
+#   30.6s / 39.7s          host load 5-20, GOMAXPROCS 6 / 4
+#   67.3s / 97.5s          host load 5-20, GOMAXPROCS 2 / 1
+#   67.3s                  GOMAXPROCS 4 at deliberate host load 52-68
+#
+# The old 30s budget was breached by every loaded run and by every GOMAXPROCS
+# at or below 6; at GOMAXPROCS 4 it failed outright ("panic: test timed out
+# after 30s"), reproduced on 33e4fa4 with no other change.
+#
+# 90s matches the org-wide backstop in REPO_POLICIES.md and is sized here
+# against the figures above: the worst case under native parallelism is 49.0s,
+# and the compound GOMAXPROCS-4-under-load case at 67.3s sits at 75% of it.
+# The one figure above 90s is GOMAXPROCS 1, a synthetic core floor rather than
+# a condition CI runs under. If a CPU-limited runner ever puts a real run near
+# 67s, that is the datum to revisit the org figure with.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    go test -v -race -timeout 30s ./...
+    go test -v -race -timeout 90s ./...
 }
 
 main "$@"