feat(design): apply Monolith Editorial design system to all Fase 1 screens

- Remove all 1px border separators (sidebar border-r, page header border-b,
  section border-t, member list divide-y, invite card border). Separation is
  now achieved via background color shifts and whitespace per the "No-Line" rule.
- Fix sidebar: bg-surface-raised vs bg-background creates tonal separation.
- Correct dark background to #020617 (slate-950) per spec.
- Add surface-container-low, text-primary/secondary/muted, destructive tokens.
- Fix CSS variable color space: all tokens are RGB triplets; switch Tailwind
  config and app.css from hsl() to rgb() to prevent yellow/warm color bleed.
- Replace emoji nav icons with Lucide icons at 16px / 1.5 stroke-width.
- Apply Masthead typography (uppercase Label-MD + Title-LG) to all page headers
  and section labels across lists, tasks, notes, search, settings, manage.
- Destructive action (sign out) uses bg-destructive per spec.
- Add `just serve` command: builds and runs the prod Node server at :3000
  against the dev Docker stack for production build testing.
- Add nav_collective i18n key (en + es).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -29,6 +29,9 @@ importers:
       idb:
         specifier: ^8.0.1
         version: 8.0.3
+      lucide-svelte:
+        specifier: ^1.0.1
+        version: 1.0.1(svelte@5.55.3)
       svelte-dnd-action:
         specifier: ^0.9.51
         version: 0.9.69(svelte@5.55.3)
@@ -2383,6 +2386,11 @@ packages:
   lru-cache@5.1.1:
     resolution: {integrity: sha512-KpNARQA3Iwv+jTA0utUVVbrh+Jlrr1Fv0e56GGzAFOXN7dk/FviaDW8LHmK52DlcH4WP2n6gI8vN1aesBFgo9w==}
 
+  lucide-svelte@1.0.1:
+    resolution: {integrity: sha512-WvzZgk0pqzgda+AErLvgWxHkfg/+GgUwqKMRHvzt0IqyMdmyEDzDCk3Z+Wo/3y753oIgx8u9Q4eUbWkghFa8Jg==}
+    peerDependencies:
+      svelte: ^3 || ^4 || ^5.0.0-next.42
+
   magic-string@0.25.9:
     resolution: {integrity: sha512-RmF0AsMzgt25qzqqLc1+MbHmhdx0ojF2Fvs4XnOqz2ZOBXzzkEwc/dJQZCYHAn7v1jbVOjAZfK8msRn4BxO4VQ==}
 
@@ -5844,6 +5852,10 @@ snapshots:
     dependencies:
       yallist: 3.1.1
 
+  lucide-svelte@1.0.1(svelte@5.55.3):
+    dependencies:
+      svelte: 5.55.3
+
   magic-string@0.25.9:
     dependencies:
       sourcemap-codec: 1.4.8