Fix app freeze on empty search results

[wesm]

Summary

• Fix command palette freeze when a search query returns zero results (e.g. "spamalot")
• Root cause: Go nil slice serializes as JSON null, not []. The frontend crashed on null.length, breaking the component and its Escape handler.
• Server now coerces nil results to an empty slice before serialization
• Frontend adds ?? [] null-coalesce as defense in depth

Test plan

• New TestSearch_ZeroResults server test asserts results is [] not null
• Existing search store tests pass
• Manual: open command palette, search for a term with no matches, verify "No results" shown and Escape works

Fixes #34

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (b847e64)

Verdict: All reviewers agree the code is clean and introduces no functional or security issues.

The changes successfully normalize empty search results from null to [] across both the frontend and backend, preventing application freezes and ensuring consistent data handling. No medium, high, or critical vulnerabilities or defects
were found.

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Synthesized from 4 reviews (agents: codex, gemini | types: default, security)