GroupVerify: Verification page, overrides and public Verified tags

Shown only where GroupVerify is: staff get the Verification page once its gv_* tables are in
the database, and the public site shows "Verified" only while it's on (enabled, with a group)
and not missing from css_plugins list, which the poller reads once a minute over RCON.

- Verification page: plugin state and version, Steam group, saved member list, overrides.
- Overrides (@zio/verify, not on yourself unless Root): give, change, remove; player drawer
  shows why a player is or isn't verified.
- Root sets the group and turns it on/off: saved to gv_settings, and sent as css_gv_* when the
  plugin is loaded so it applies at once.
- gv_* times use GroupVerify's own timezone setting.
- MySQL integration test (SAW_TEST_DSN), unit tests for plugin list parsing and the show rule.

internal/web/assets/styles.css

@@ -427,6 +427,7 @@ td.num, th.num { text-align: right; white-space: nowrap; }
 .tag.red { background: var(--accent-soft); color: #ff5a78; }
 .tag.amber { background: var(--amber-soft); color: var(--amber); }
 .tag.green { background: var(--green-soft); color: var(--green); }
+.tag.verified { background: rgba(79, 179, 217, .14); color: #4fb3d9; }
 
 .rank {
   display: inline-flex;