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/CanaryTokenDrawer.tsx

@@ -44,7 +44,7 @@ interface Props {
 }
 
 const Row: React.FC<{ label: string; value: React.ReactNode }> = ({ label, value }) => (
-  <div style={{ display: 'flex', gap: '12px', padding: '6px 0', borderBottom: '1px solid rgba(255,255,255,0.05)' }}>
+  <div style={{ display: 'flex', gap: '12px', padding: '6px 0', borderBottom: '1px solid var(--matrix-tint-5)' }}>
     <div style={{ minWidth: '140px', color: 'var(--dim-color)', fontSize: '0.75rem', textTransform: 'uppercase' }}>{label}</div>
     <div style={{ flex: 1, fontSize: '0.85rem', wordBreak: 'break-all' }}>{value ?? <span style={{ opacity: 0.4 }}>—</span>}</div>
   </div>
@@ -291,8 +291,8 @@ const CanaryTokenDrawer: React.FC<Props> = ({ token, onClose, onRevoked }) => {
                 key={t.uuid}
                 style={{
                   padding: '8px 12px',
-                  border: '1px solid rgba(255,255,255,0.08)',
-                  background: 'rgba(255,255,255,0.02)',
+                  border: '1px solid var(--matrix-tint-5)',
+                  background: 'var(--matrix-tint-5)',
                   fontSize: '0.8rem',
                 }}
               >