Remove dead code: splitLines loop, unused methods (gt-2g130)

- polecat.go: Remove unreachable first loop in splitLines (was using filepath.SplitList incorrectly)
- townlog/logger.go: Remove unused Event.JSON() method and json import
- lock/lock.go: Remove unused ErrStaleLock error variable
- refinery/manager.go: Remove unused getTestCommand() method

Note: witness.StatePaused is actually used by cmd/witness.go, not dead code.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/lock/lock.go

@@ -22,10 +22,9 @@ import (
 
 // Common errors
 var (
-	ErrLocked       = errors.New("worker is locked by another agent")
-	ErrNotLocked    = errors.New("worker is not locked")
-	ErrStaleLock    = errors.New("stale lock detected")
-	ErrInvalidLock  = errors.New("invalid lock file")
+	ErrLocked      = errors.New("worker is locked by another agent")
+	ErrNotLocked   = errors.New("worker is not locked")
+	ErrInvalidLock = errors.New("invalid lock file")
 )
 
 // LockInfo contains information about who holds a lock.