feat(tui): persist model tier selection and fix formatting

Persist /model tier choice to ~/.local/share/flynn/preferences.json so
it survives restarts. Decode HTML entities (e.g. ') in markdown
renderer output. Suppress noisy logger.info and punycode deprecation
warnings in TUI startup.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/frontends/tui/markdown.test.ts

@@ -109,4 +109,10 @@ describe('renderMarkdown', () => {
     expect(result).toContain('\x1b[34m');
     expect(result).toContain('https://example.com');
   });
+
+  it('decodes HTML entities like apostrophes', () => {
+    const result = renderMarkdown("I'm here. What's up?");
+    expect(result).toContain("I'm here");
+    expect(result).not.toContain(''');
+  });
 });