feat(sessions): masquer les sessions externes + terminal plein écran

Masquage persistant des sessions Claude découvertes (lancées hors Arboretum)
qui polluent la liste — calqué sur repos.hidden :
- table hidden_sessions (#9) clé claudeSessionId ; helpers DB
- DiscoveryService pose le champ additif SessionSummary.hidden (resume/fork
  restent possibles, survit à un re-scan)
- routes POST/DELETE /sessions/:id/hide, POST /sessions/hide-discovered
  (masse, un clic), GET /sessions?includeHidden=true
- UI : bouton Masquer par ligne, « Masquer l'historique externe », toggle
  « Afficher les masquées », badge masquée ; store + i18n EN/FR + audit

Terminal plein écran (corrige le sizing) :
- SessionView root s'étire (flex-1) → xterm calcule les bonnes dimensions
- refit robuste (requestAnimationFrame + après resync), h-full sur le wrapper
- bouton plein écran (API Fullscreen), tabbar mobile masquée en fullbleed

DialogPrompt : options en liste verticale pleine largeur (plus de troncature
ni de chevauchement sur les libellés longs / multi-lignes).

Doc : centre d'aide (sessions), README EN/FR, site (showcase), CLAUDE.md.
Tests : discovery (hidden) + route hide/unhide/hide-discovered.

packages/site/src/i18n/en.ts

@@ -35,11 +35,11 @@ export default {
   scAKicker: 'Worktree-first dashboard',
   scATitle: 'See what needs you — before anything stalls',
   scABody:
-    'A live list of every worktree and its session state. The Needs attention rail floats the agents waiting on a decision to the top, so nothing sits blocked while you are heads-down elsewhere.',
+    'A live list of every worktree and its session state. The Needs attention rail floats the agents waiting on a decision to the top, so nothing sits blocked while you are heads-down elsewhere. Hide the noisy history left by past terminal sessions so the list stays actionable.',
   scBKicker: 'Multi-terminal grid',
   scBTitle: "Every agent's output, streaming live",
   scBBody:
-    'Watch all your sessions at once — real terminal output, color-coded by state, updating in real time. Click any pane to take over, answer a prompt, or stop a run.',
+    'Watch all your sessions at once — real terminal output, color-coded by state, updating in real time. Click any pane to take over in a fullscreen terminal — prompt pinned to the bottom, full scrollback above — answer a prompt, or stop a run.',
   scCKicker: 'On your phone',
   scCTitle: 'Unblock an agent from the kitchen',
   scCBody: