lib/common: safely expand arrays in strict mode

[jamesacklin]

Hello! I ran into this issue with the /hivemind-search command:

Bash(~/.claude/skills/hivemind-search/search.sh "passkeys")                                                                                               
  ⎿  Error: Exit code 1                                                                                                                                     
     /Users/jamesacklin/.claude/skills/hivemind-search/../lib/hivemind-common.sh: line 146: curl_args[@]: unbound variable

The issue occurs when curl_args is an empty array and bash is running in strict mode with set -u (which treats unset/empty variables as errors).

This proposes conditional expansion, which means if curl_args has elements, we expand them with proper quoting. If it's empty, we expand to nothing (no error).

[givenness]

+1 ran into this issue as well