feat(v0.2): tab title = current folder (from OSC title)

- title-util.ts: folderFromTitle() parses 'user@host:~/path' → last folder
  segment (home stays ~); pure, dependency-free, 7 unit tests
- terminal-session.ts: onTitleChange → folderFromTitle so the tab auto-names
  to the cwd folder and updates live on cd
- Browser-verified: ~ → cd project → 'web-terminal' → cd docs → 'docs' → cd ~ → '~'.
  198 tests green, typecheck + build ok.

public/terminal-session.ts

@@ -11,6 +11,7 @@
 import { Terminal } from '@xterm/xterm'
 import { FitAddon } from '@xterm/addon-fit'
 import type { ClientMessage, ServerMessage } from '../src/types.js'
+import { folderFromTitle } from './title-util.js'
 
 const RESET = '\x1b[0m'
 const BOLD = '\x1b[1m'
@@ -94,7 +95,8 @@ export class TerminalSession {
     this.term.open(this.el)
 
     this.term.onData((data) => this.send(data))
-    this.term.onTitleChange((title) => this.onTitle?.(title))
+    // Tab title = current folder, derived from the shell's OSC title.
+    this.term.onTitleChange((title) => this.onTitle?.(folderFromTitle(title) ?? title))
 
     this.resizeObserver = new ResizeObserver(() => this.scheduleResize())
     this.resizeObserver.observe(this.el)