fix: exit webedit when port is already in use

[joeblew999]

Summary

Fixes #16

Previously, when the server port was already in use, toki webedit would log an error but continue running indefinitely, waiting for an interrupt signal. This was confusing as the UI wouldn't open but the process wouldn't exit.

Now the server uses a channel to signal startup errors back to the main goroutine, which properly exits with an error message when the port is unavailable.

Changes

• Added serverErr channel to communicate server startup failures
• Changed from blocking on interrupt signal only to select on both interrupt and server error
• Returns proper error when port is in use instead of hanging

Test

# Start something on port 52000
python3 -m http.server 52000 &

# Try webedit - now exits with error instead of hanging
toki webedit -host :52000 -dontopen
# Output: [ERROR] server failed to start: listen tcp :52000: bind: address already in use