test: add comprehensive test coverage (35% → 58%, threshold 50%)

Add 180+ new tests across 10 test files covering previously untested modules:
- instructions_cli (0% → 100%), hooks_cli (73% → 96%), spellcheck (28% → 84%)
- palace_graph (9% → 91%), general_extractor (0% → 92%), entity_detector (0% → 69%)
- entity_registry (0% → 70%), room_detector_local (0% → 55%), layers (0% → 28%)
- onboarding (0% → 36%)

Also fixes Windows encoding bug in onboarding.py (write_text without encoding="utf-8").

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_instructions_cli.py

@@ -0,0 +1,45 @@
+"""Tests for mempalace.instructions_cli — instruction text output."""
+
+from unittest.mock import patch
+
+import pytest
+
+from mempalace.instructions_cli import AVAILABLE, INSTRUCTIONS_DIR, run_instructions
+
+
+def test_run_instructions_valid_name(capsys):
+    """Valid name prints the .md file content."""
+    name = "init"
+    expected = (INSTRUCTIONS_DIR / f"{name}.md").read_text()
+    run_instructions(name)
+    captured = capsys.readouterr()
+    assert captured.out.strip() == expected.strip()
+
+
+def test_run_instructions_all_available(capsys):
+    """Every name in AVAILABLE should succeed without error."""
+    for name in AVAILABLE:
+        run_instructions(name)
+        out = capsys.readouterr().out
+        assert len(out) > 0
+
+
+def test_run_instructions_invalid_name(capsys):
+    """Invalid name should sys.exit(1) and print error to stderr."""
+    with pytest.raises(SystemExit) as exc_info:
+        run_instructions("nonexistent")
+    assert exc_info.value.code == 1
+    captured = capsys.readouterr()
+    assert "Unknown instructions: nonexistent" in captured.err
+    assert "Available:" in captured.err
+
+
+def test_run_instructions_missing_md_file(capsys, tmp_path):
+    """If the .md file is missing on disk, should sys.exit(1)."""
+    with patch("mempalace.instructions_cli.INSTRUCTIONS_DIR", tmp_path):
+        with patch("mempalace.instructions_cli.AVAILABLE", ["fakecmd"]):
+            with pytest.raises(SystemExit) as exc_info:
+                run_instructions("fakecmd")
+            assert exc_info.value.code == 1
+            captured = capsys.readouterr()
+            assert "Instructions file not found" in captured.err