Update launcher with experimental VNC mode (reflect issue #9)

[hmmhmmhm]

This PR reflects and operationalizes the proposal in issue #9 (update to vphone-cli).

Why this PR:

• I observed that VNC performance was often slow in real use (latency/input responsiveness).
• While searching for improvements, I found a strong proposal in issue update to vphone-cli #9.
• I tested that approach locally, and it worked very well in practice.

Expected impact:

• Better VNC responsiveness and more reliable keyboard/hotkey behavior.
• Keep the default path unchanged unless explicitly enabled.

Issue reference:

• update to vphone-cli #9

What changed:

1. Add experimental vnc source overrides

• add experimental-vnc/ overrides for vphone-cli sources
• include helper script experimental-vnc/enable.sh

2. Update launcher for experimental vnc mode

• add optional launcher path via env var:
  • VPHONE_VNC_EXPERIMENTAL=1 ./vphone-aio.sh
• launcher applies source overrides before boot
• fix option conflict so --vnc-experimental is applied correctly
• set experimental mode defaults:
  • VPHONE_VNC_PORT=5901
  • VPHONE_VNC_PASSWORD=alpine

3. Update readme for experimental vnc mode

• document usage and runtime output
• document fixed defaults and env override behavior

Connection method changes when experimental mode is enabled:

• Default mode (unchanged): connect to fixed vnc://127.0.0.1:5901
• Experimental mode (default values): connect with vnc://:alpine@127.0.0.1:5901
• You can still override via env:
  • VPHONE_VNC_PORT
  • VPHONE_VNC_PASSWORD

Notes:

• Commit structure follows existing short imperative style.
• This keeps default behavior unchanged unless the env var is enabled.