feat(project): add project trust and restricted execution mode (#517)

Projects now open with a user-owned trust decision. The prompt offers Preview in Restricted Mode, Don't Open and Trust Project, with an optional trusted parent folder; preview is the default focus so Enter never grants trust.

Restricted projects keep browsing, editing, saving, search and highlighting. Project-controlled execution is denied by default in the backend: run, debug, build, tools, language servers, plugins and Git commands that could honour repository configuration. Trusting a project enables those paths without reopening it, and decisions can be revoked in Settings.

Terminals stay available when the user opens one, without project shell settings, environment or virtualenv activation. A shell prompt that runs git in the folder can still honour the repository's core.fsmonitor.

Fixes #462

src/ui/Dialog.module.css

@@ -231,6 +231,11 @@
 .messageIcon {
   flex: none;
 }
+.messageAppIcon {
+  flex: none;
+  width: 64px;
+  height: 64px;
+}
 .messageShape {
   fill: var(--message-icon-color);
 }