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>

apps/web/messages/en.json

@@ -5,6 +5,7 @@
 	"nav_notes": "Notes",
 	"nav_search": "Search",
 	"nav_settings": "Settings",
+	"nav_collective": "Collective",
 	"app_name": "Colectivo",
 	"loading": "Loading…",
 	"error_generic": "Something went wrong. Please try again.",

apps/web/messages/es.json

@@ -5,6 +5,7 @@
 	"nav_notes": "Notas",
 	"nav_search": "Buscar",
 	"nav_settings": "Ajustes",
+	"nav_collective": "Colectivo",
 	"app_name": "Colectivo",
 	"loading": "Cargando…",
 	"error_generic": "Algo salió mal. Por favor, inténtalo de nuevo.",