Shell: Tab completes a path on the SD card (#67)

Past the command's name, Tab completes the word being typed as a path: a
folder keeps its slash to go on from, a file completed whole gets a space,
several candidates are listed. Any case typed, the name's own is taken.
After a file command the first slash is understood (`cat no` is /no).
The folder is read on the storage task, bounded to 400 entries looked at
and 24 candidates.

489 host tests (2 new). Checked on the device: a folder, a file inside it,
several candidates, no slash, another case, nothing matching.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/apps/shell_app.cpp

@@ -123,13 +123,16 @@ bool ShellApp::onKey(const KeyEvent& e) {
         case Key::Down:
             if (history_.down(recalled)) input_.setText(recalled);
             break;
-        case Key::Tab: {
+        case Key::Tab: {  // the command's name, or past it a path on the card
             std::vector<std::string> matches;
-            input_.setText(completeCommand(input_.text(), words_, matches));
+            PathToComplete path;
+            bool more = false;
+            if (splitForPath(input_.text(), path)) input_.setText(completePath(path, list_(path.folder, path.prefix, more), matches));
+            else input_.setText(completeCommand(input_.text(), words_, matches));
             if (matches.size() > 1) {
                 std::string all;
                 for (auto& m : matches) all += (all.empty() ? "" : "  ") + m;
-                log_.add(all);
+                log_.add(all + (more ? "  ..." : ""));
             }
             break;
         }