fix(decnet_web/css): sweep rgba colour literals to tokens app-wide

Pre-this-commit, ~80 rgba() literals across 24 files were
hardcoding alert-red, warn-amber, info-cyan, panel-dark, and
white-text-with-alpha shades that bypassed the token cascade.
Net effect in light mode: the .eml/SESSREC drawers, AttackerDetail
verdict pills, MazeNET net-box headers, OPEN/REPLAY action
buttons, threat-intel cards, and all the dim 'whitish' overlays
stayed on their dark-mode hex values, producing the unreadable
panels in the screenshots.

Sweep maps each rgba colour family onto the existing token by
alpha bucket — rgba(13,17,23,*) -> var(--panel),
rgba(255,65,65,*) -> var(--alert)/-tint-10,
rgba(255,170,0,*) and rgba(224,160,64,*) -> var(--warn)/-tint-10,
rgba(0,200,255,*) -> var(--info)/-tint-10,
rgba(255,255,255,*) -> var(--fg-N)/var(--matrix-tint-N) by alpha.

VERDICT_TONE in AttackerDetail (MALICIOUS/SUSPICIOUS/BENIGN/
NO SIGNAL) was the worst offender — string literals
'#ff4d4d'/'#ffae42'/'#5fd07a'/rgba(255,255,255,0.4) baked into
inline JS styles. Now resolves at render time via var(--alert)/
var(--warn)/var(--ok)/var(--fg-4).

New tokens in :root:
 - --bg-color (alias of --bg) — drawers used this name with
   #0d1117 fallback that fired in every browser because nothing
   defined --bg-color. Adding the alias makes drawers re-tone.
 - --info / --info-tint-10 / --info-tint-30 — REPLAY buttons and
   any future neutral-secondary use.
 - --ok — semantic alias for 'verified good' (matrix in dark,
   emerald in light) so BENIGN pills stay readable across themes.

Login.css left intentionally — pre-auth surface, not themed.

decnet_web/src/components/Config.css

@@ -165,7 +165,7 @@
 .action-btn.danger:hover {
   background: #ff4141;
   color: var(--background-color);
-  box-shadow: 0 0 10px rgba(255, 65, 65, 0.5);
+  box-shadow: 0 0 10px var(--alert);
 }
 
 /* Add User Form */
@@ -260,7 +260,7 @@
   font-size: 0.75rem;
   padding: 6px 12px;
   border: 1px solid #ff4141;
-  background: rgba(255, 65, 65, 0.1);
+  background: var(--alert-tint-10);
   display: inline-block;
 }