Read hook payload from fd 0, not /dev/stdin

Claude Code delivers the hook payload on a socket. Opening it by path
('/dev/stdin' -> /proc/self/fd/0) fails with ENXIO, so bash-guard.mjs threw on
every invocation and its bare catch exited 0 silently. The guard looked like it
was never dispatched; it was dying on line 29 each time.

readFileSync(0) is read() on the descriptor with no open(), which works on a
socket. The catch now logs instead of swallowing, so this failure mode can never
again masquerade as non-dispatch.

Adds test-bash-guard.py, which drives the guard over a socketpair. A pipe would
not reproduce the bug, so the socket is load-bearing. Verified failing against
the pre-fix guard (silent, no output) and passing after.

Removes the five diagnostic probes and probe.mjs; they served their purpose.
Bumps to 1.0.2 because the plugin cache is keyed by version and an unchanged
version silently skips reinstall.

plugins/guards/hooks/hooks.json

@@ -11,46 +11,6 @@
             "statusMessage": "Checking jj/attribution policy; gating push on build + tests..."
           }
         ]
-      },
-      {
-        "matcher": "Bash",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/probe.mjs\" P1-plain"
-          }
-        ]
-      },
-      {
-        "matcher": "Bash",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/probe.mjs\" P2-timeout-only",
-            "timeout": 600
-          }
-        ]
-      },
-      {
-        "matcher": "Bash",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/probe.mjs\" P3-status-only",
-            "statusMessage": "probe P3 status-only"
-          }
-        ]
-      },
-      {
-        "matcher": "Bash",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/probe.mjs\" P4-both",
-            "timeout": 600,
-            "statusMessage": "probe P4 both"
-          }
-        ]
       }
     ],
     "PostToolUse": [
@@ -63,16 +23,6 @@
             "timeout": 5
           }
         ]
-      },
-      {
-        "matcher": "Write|Edit|MultiEdit",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/probe.mjs\" P5-post-status",
-            "statusMessage": "probe P5 post status"
-          }
-        ]
       }
     ]
   }