v0.8.30 — GBK console crash fix, add --stdio validation, serve --http address

Added

• Zero-config demo on the empty-state card. A machine with no MCP servers used
  to be told "next: mcptoon quickstart" — but quickstart discovers servers and
  there are none to find, a dead end. The first-run card now leads with
  mcptoon demo (it spins up its own 22-tool server and shows the before/after in
  ~10s, zero config), then offers quickstart as the discovery step.
• docs/real-world-benchmark.md — 7 real public MCP servers / 209 tools measured
  on a real machine: 640,606 → 905 tokens (−99.86%), reproducible with mcptoon bench. Answers the "the 99.2% is a synthetic 255-tool sample" objection; linked
  from both READMEs.

Fixed

• Commands no longer crash on a non-UTF-8 (GBK) console. mcptoon prints glyphs
  (✓ 🎉 ⚠ ❌ →). On a default Chinese Windows console (cp936/GBK, Python's legacy
  mode), status, doctor, footer-facts, quickstart, demo, sync and off
  raised UnicodeEncodeError: 'gbk' codec can't encode character — a raw traceback
  and exit 1. A startup guard now reconfigures stdout/stderr: on a tty it keeps the
  console's encoding but adds errors="replace" (localized text stays readable);
  when piped or redirected it switches to UTF-8 with errors="replace". Either way
  a glyph the codec lacks becomes a placeholder instead of a crash.
• mcptoon add --stdio catches a command that can never launch. A path the user
  wrote that does not exist (add broken --stdio C:\no\such.exe) used to print
  "Added server 'broken'" and exit 0; the breakage surfaced only on the next command
  as an opaque [WinError 2] that never named the file. It now hard-errors on a
  missing explicit path (with --force to override) and warns when a bare command
  name is not on PATH (still added — it may be installed later).
• serve --http <addr> honours the address. serve --background --http :18099
  silently kept the :8080 shorthand and then failed "8080 is already in use",
  never mentioning the requested port. --http now takes a following address (or
  --http=<addr>); the bare --http shorthand is still :8080.

Changed

• README (en + zh): one line under the install command noting the built-in
  "new version available" hint and mcptoon upgrade.