feat(welcome): New project flow + per-repo account roadblock (T-488)

The UI half of the new-project flow (story T-486). A "New project…" welcome
action opens a dialog (location + name) that dispatches project.new (T-487),
opens the result, and announces it on projectCreatedChannel. The Claude
extension consumes that and shows the account roadblock — the embedded
per-workspace picker + accounts list, so a fresh project gets bound to an
account (or Default) right at birth.

The two halves stay decoupled: the welcome builtin only publishes the event
(no claude import); the claude builtin owns the account dialog. Only freshly-
created projects announce, so existing opens are never prompted.

Closes T-488. The non-repo "initialize as a project" path (T-489) is next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/i18n/en_us/builtin.welcome.json

@@ -14,6 +14,11 @@
   "tips.findInFiles": { "translation": "Find in files" },
   "tips.focusMode": { "translation": "Focus mode" },
   "action.openFolder": { "translation": "Open folder…" },
+  "action.newProject": { "translation": "New project…" },
+  "dialog.newProject.title": { "translation": "New project" },
+  "dialog.newProject.body": { "translation": "Creates a git repo + a CLAUDE.md, then opens it." },
+  "button.create": { "translation": "Create" },
+  "button.creating": { "translation": "Creating…" },
   "recent.empty": { "translation": "No recent projects." },
   "sticky.label": { "translation": "always open this project on launch" },
   "sticky.tooltip": { "translation": "Always open this project on launch" },

assets/i18n/nl_nl/builtin.welcome.json

@@ -14,6 +14,11 @@
   "tips.findInFiles": { "translation": "Zoeken in bestanden" },
   "tips.focusMode": { "translation": "Focusmodus" },
   "action.openFolder": { "translation": "Map openen…" },
+  "action.newProject": { "translation": "Nieuw project…" },
+  "dialog.newProject.title": { "translation": "Nieuw project" },
+  "dialog.newProject.body": { "translation": "Maakt een git-repo + een CLAUDE.md, en opent het." },
+  "button.create": { "translation": "Aanmaken" },
+  "button.creating": { "translation": "Aanmaken…" },
   "recent.empty": { "translation": "Geen recente projecten." },
   "sticky.label": { "translation": "dit project altijd openen bij opstarten" },
   "sticky.tooltip": { "translation": "Dit project altijd openen bij opstarten" },