Implement runit support for Fenris monitoring (issue #84)

Deliver end-to-end native monitoring path under runit with existing
CLI/TUI controls and truthful status, preserving systemd behavior.

Changes:
- Add init system abstraction layer (src/fenris/init_system.py) that
  detects systemd vs runit and provides unified interface for timer
  control, on-demand collection, and service state queries
- Create runit service files (units/runit/) with completion-relative
  5-minute cadence, 2-minute boot delay, bounded execution (90s),
  no catch-up, and serialized runs via flock
- Update monitor.py to use abstraction layer instead of direct systemctl
- Update status.py to use abstraction layer for service state queries
- Update all packaging scripts (deb, rpm) for init-system-aware setup
- Update Makefile to install runit service files alongside systemd units
- Add 46 tests for init system abstraction layer

Spec: ADR 0008, §8.4, §8.5, §8.6, §8.7, §8.8
Closes #84

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

tests/test_monitor.py

@@ -56,8 +56,7 @@ class TestEnableIdempotentMatrix:
         """A fresh package install has a store directory but no database yet."""
         args = MagicMock(now=False, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.enable_timer") as mock_enable:
             cmd_enable(args)
 
         conn = init_store(store_path)
@@ -74,8 +73,7 @@ class TestEnableIdempotentMatrix:
         
         args = MagicMock(now=False, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.enable_timer") as mock_enable:
             cmd_enable(args)
 
         # Period should be open
@@ -100,8 +98,7 @@ class TestEnableIdempotentMatrix:
 
         args = MagicMock(now=True, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.enable_timer") as mock_enable:
             cmd_enable(args)
 
         # Should still have exactly one open period
@@ -125,8 +122,7 @@ class TestEnableIdempotentMatrix:
 
         args = MagicMock(now=True, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.enable_timer") as mock_enable:
             cmd_enable(args)
 
         # Should have a new open period
@@ -155,8 +151,7 @@ class TestDisableIdempotentMatrix:
 
         args = MagicMock(now=True, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.disable_timer") as mock_disable:
             cmd_disable(args)
 
         # Period should be closed with user_disabled
@@ -174,8 +169,7 @@ class TestDisableIdempotentMatrix:
 
         args = MagicMock(now=True, store_path=store_path)
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.disable_timer") as mock_disable:
             cmd_disable(args)
 
         # No periods should exist
@@ -207,28 +201,19 @@ class TestDisableIdempotentMatrix:
 class TestCollectTrigger:
     """§8.7: On-demand collection via helper path."""
 
-    def test_collect_triggers_systemctl_start(self):
-        """Collect starts fenris-collect.service synchronously."""
+    def test_collect_triggers_init_system(self):
+        """Collect triggers init_system.collect_now."""
         args = MagicMock()
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(returncode=0)
+        with patch("fenris.monitor.collect_now") as mock_collect:
             cmd_collect(args)
-
-        mock_sub.run.assert_called_once_with(
-            ["systemctl", "start", "fenris-collect.service"],
-            capture_output=True,
-            text=True,
-        )
+            mock_collect.assert_called_once()
 
     def test_collect_failure_exits_nonzero(self):
         """Collect failure exits with nonzero status."""
         args = MagicMock()
 
-        with patch("fenris.monitor.subprocess") as mock_sub:
-            mock_sub.run.return_value = MagicMock(
-                returncode=1, stderr="Unit not found"
-            )
+        with patch("fenris.monitor.collect_now", side_effect=SystemExit(1)):
             with pytest.raises(SystemExit) as exc_info:
                 cmd_collect(args)
             assert exc_info.value.code == 1