Change reconnectMu from sync.Mutex to sync.RWMutex so read operations
can hold RLock during database access. This prevents reconnect() from
closing the connection while queries are in progress.
- GetIssue and SearchIssues now hold RLock during database operations
- Close() acquires write lock to coordinate with reconnect
- Add TestConcurrentReadsWithReconnect to verify the fix
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>