Harden server bind failures (port retry confusion)

[blinkerbit]

Source: gitlab-issues-export.md (Issue 6)

Weight: 2

Problem / context

_start_server in aird/main.py retries on bind failure with port increment; operators can land on an unexpected port or miss the root cause (permissions vs EADDRINUSE).

Suggested approach / acceptance criteria

• Log structured error (errno, message) on each failure.
• Optionally default to fail-fast unless env AIRD_PORT_RETRY=1 (or document current max retries clearly in README/config).