Let the git remote be set from Settings

Attaching a workspace to an existing repository meant leaving for a
terminal: gitsync could init, commit and push, and could tell whether an
'origin' existed, but had no way to create one, and nothing in the
settings held a remote URL. Sync just logged "no 'origin' remote
configured" and committed locally.

Settings > Git remote... now shows the workspace repository's origin and
lets it be set, repointed or cleared. The URL is read from and written
to the repository, never to config.json, because a remote belongs to the
checkout — so each workspace shows its own, and the box is refreshed
whenever the repository in play changes.

This is separate from the Gitea publishing in New project, which is a
cookiecutter post-gen hook and only ever applies to generated projects.

Also factors out first_output_line, which repo_root and the new
origin_url were both open-coding, and origin_args, so the add-vs-set-url
decision can be tested without a repository on disk.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GBWj9TphFMCoh7VHaSRnvQ

src/app/mod.rs

@@ -203,6 +203,12 @@ pub struct App {
     rename_focus: bool,
     /// Whether the delete confirmation opened from that menu is up.
     confirm_delete: bool,
+    /// Editable copy of the workspace repository's `origin` URL. Read back from
+    /// git whenever the repository changes, never persisted to the config —
+    /// the remote belongs to the checkout, not to the app.
+    remote_input: String,
+    /// Whether the git-remote dialog is up.
+    show_git_remote: bool,
     status: String,
     show_log: bool,
     git_log: String,
@@ -371,6 +377,8 @@ impl App {
             show_rename: false,
             rename_focus: false,
             confirm_delete: false,
+            remote_input: String::new(),
+            show_git_remote: false,
             status: String::new(),
             show_log: false,
             git_log: String::new(),
@@ -534,6 +542,10 @@ impl eframe::App for App {
             self.confirm_delete_window(ctx);
         }
 
+        if self.show_git_remote {
+            self.git_remote_window(ctx);
+        }
+
         if self.show_new_project {
             self.new_project_window(ctx);
         }