feat(server): support bounded port ranges

[iurysza]

Summary

• accept inclusive PLANNOTATOR_PORT ranges such as 19432-19463
• try each port in order and bind the first available one in Bun and Pi runtimes
• preserve existing fixed-port retries and random-port defaults

Validation

• focused port tests: 42 passed, 0 failed
• syntax bundle of all changed runtime files
• git diff --check

Related to #899

[backnotprop]

thanks, in review