feat: brand icons for widgets, fix stale accent color

Two separate issues, both real bugs:

- Dark mode was showing light blue instead of green: config.yml still
  had a leftover --pn-accent: #38bdf8 override from before the design
  redesign, which won via the runtime theme injector regardless of
  what app/globals.css defaulted to. Removed the override and pushed
  the dark-mode default from a soft mint (#5ee08c) to an actual neon
  green (#39ff88) - closer to what "neon" means and closer to the real
  phosphor-green a cardiac monitor trace uses, which fits the pulse
  metaphor better than the pastel version did.

- No per-service brand icons anywhere. Added an optional `icon` field
  to docker/bookmark widgets (a key into lib/brand-icons.ts) rather
  than guessing from containerName, since a heuristic would silently
  misfire for anyone's own container naming. database widgets derive
  their icon automatically from `engine` (postgres/redis) since that's
  already required and unambiguous. Icon path data comes from the CC0
  simple-icons package via scripts/extract-brand-icons.py, extracted
  and committed as plain TS data (lib/brand-icons.ts) rather than
  imported live - keeps it self-hosted (no unpkg.com/CDN calls at
  runtime, matching the fonts) and pinned regardless of dependency
  updates. Rendered monochrome (currentColor, not each brand's own
  hex) to stay consistent with the single-accent design rather than a
  dozen competing colors - only the shape carries the identity.

Wired real icons into config.yml for every service that has one:
traefik, coolify, gitea (+ gitea_runner), immich (+ immich_ml), n8n,
passbolt, umami, headscale, plus postgresql/redis on every database
widget. code and mailpit have no brand match in the curated set, so
they render without one rather than a wrong/generic substitute.

Verified in the actual rendered page: compiled CSS confirms
--pn-accent is #39ff88 (dark) / #339a5a (light) with no trace of the
old #38bdf8, and all 18 expected icon instances (10 docker + 8
database widgets) are present.

pnpm-lock.yaml

@@ -32,6 +32,9 @@ importers:
       react-dom:
         specifier: 19.2.8
         version: 19.2.8(react@19.2.8)
+      simple-icons:
+        specifier: ^16.28.0
+        version: 16.28.0
       systeminformation:
         specifier: ^5.33.1
         version: 5.33.1
@@ -2213,6 +2216,10 @@ packages:
     resolution: {integrity: sha512-6x6dK6zJdpTzF4sQeNYxwtvBzf6Eg4GtlesS94HOvTudUeyK2WXAaIfmDgsyslYrRBeFIlsi54AYsFGUuhmvrQ==}
     engines: {node: '>= 0.4'}
 
+  simple-icons@16.28.0:
+    resolution: {integrity: sha512-sQPR5AtK/ijRjou7zw7mlLp08oB6FH7i0lOy5XJ2zp9mJs/yejgiOn7KvQoe2q4YJIx6VmgUSW5AOefebPt5kg==}
+    engines: {node: '>=0.12.18'}
+
   source-map-js@1.2.1:
     resolution: {integrity: sha512-UXWMKhLOwVKb728IUtQPXxfYU+usdybtUrK/8uGE8CQMvrhOpwvzDBwj0QhSL7MQc7vIsISBG8VQ8+IDQxpfQA==}
     engines: {node: '>=0.10.0'}
@@ -4716,6 +4723,8 @@ snapshots:
       side-channel-map: 1.0.1
       side-channel-weakmap: 1.0.2
 
+  simple-icons@16.28.0: {}
+
   source-map-js@1.2.1: {}
 
   split-ca@1.0.1: {}