feat(update): background update check with post-command notice

[eddietejeda]

Summary

• Spawns the GitHub release check in a background thread before the command runs, so the network call overlaps with command execution
• Joins the result after the command finishes via recv_timeout(6s), ensuring the notice always appears at the bottom of output
• Uses mpsc::Receiver instead of JoinHandle::join to avoid indefinite blocking if the HTTP request stalls past its own 5s timeout
• Unifies the upgrade message to hotdata update for all install methods (drops the Homebrew-specific branch in the notice)

Test plan

• Run any command (e.g. hotdata query status <id>) when a newer version exists — notice appears after command output in yellow
• Run hotdata update — no notice printed (skipped for the update command itself)
• Set HOTDATA_NO_UPDATE_CHECK=1 — no notice printed
• Run in a non-TTY context (e.g. pipe output) — no notice printed
• Simulate a slow/hanging network: notice is skipped gracefully after 6s, command still exits cleanly

🤖 Generated with Claude Code

[sentry]

Codecov Report

❌ Patch coverage is 47.61905% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/update.rs	41.17%	10 Missing ⚠️
src/main.rs	75.00%	1 Missing ⚠️

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