docs: clarify uninstall run-order + statusLine ceiling

Follow-up to #228 (issue #226):

- README: state that scripts/uninstall.js must run *before* the host
  remove command, since the script is itself a plugin file and gets
  deleted by the removal (or run it from a separate clone).
- uninstall.js: add a ponytail: comment naming the statusLine match
  ceiling — substring match + whole-key delete removes a combined
  (e.g. caveman+ponytail) statusline wholesale; upgrade path noted.
- Add trailing newline to the file.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/uninstall.js

@@ -26,6 +26,10 @@ try {
   const raw = fs.readFileSync(settingsPath, 'utf8').replace(/^\uFEFF/, '');
   const settings = JSON.parse(raw);
   const cmd = settings.statusLine && settings.statusLine.command;
+  // ponytail: substring-match the script name, then drop the whole statusLine
+  // key. A combined statusline (e.g. caveman+ponytail) whose command contains
+  // "ponytail-statusline" gets removed wholesale. Parse out only ponytail's part
+  // if combined statuslines become common.
   if (typeof cmd === 'string' && cmd.includes('ponytail-statusline')) {
     delete settings.statusLine;
     fs.writeFileSync(settingsPath, JSON.stringify(settings, null, 2), 'utf8');
@@ -33,4 +37,4 @@ try {
   }
 } catch (e) {
   if (e.code !== 'ENOENT') throw e;
-}
+}