Hooks: ATC IPC layer between gcode preprocessor and runtime

Adds bbctrl.Hooks: a small dispatch layer for HOOK:<event>:<data>
messages embedded in g-code as (MSG,HOOK:droptool:) etc. Hooks can
block the unpause until the registered callback completes and
auto-resume after.

- bbctrl.Hooks: registry, fire, dispatch_hook_message, persistent
  config in hooks.json, REST surface (/api/hooks, /api/hooks/save,
  /api/hooks/status, /api/hooks/fire/<event>).
- Ctrl: instantiate self.hooks alongside the other subsystems.
- Planner._add_message: when a (MSG,...) line is HOOK:<event>:<data>,
  route it through ctrl.hooks instead of state.messages so it never
  surfaces as a UI popup and dispatch is immediate (state.messages
  has a 250ms debounce).
- Web: handlers for the /api/hooks routes.

src/py/bbctrl/Web.py

@@ -766,6 +766,27 @@ class RotaryHandler(bbctrl.APIHandler):
             log.error('Unexpected error: {}'.format(e))
 
 
+class HooksGetHandler(bbctrl.APIHandler):
+    def get(self):
+        self.write_json(self.get_ctrl().hooks.get_config())
+
+
+class HooksSaveHandler(bbctrl.APIHandler):
+    def put_ok(self):
+        self.get_ctrl().hooks.save_config(self.json)
+
+
+class HooksStatusHandler(bbctrl.APIHandler):
+    def get(self):
+        self.write_json(self.get_ctrl().hooks.get_status())
+
+
+class HooksFireHandler(bbctrl.APIHandler):
+    def put_ok(self, event):
+        data = self.json if hasattr(self, 'json') and self.json else {}
+        self.get_ctrl().hooks._fire(event, data)
+
+
 class RemoteDiagnosticsHandler(bbctrl.APIHandler):
 
     def get(self):
@@ -798,7 +819,6 @@ class RemoteDiagnosticsHandler(bbctrl.APIHandler):
                     'message': e.reason or "Unknown"
                 })
 
-
 class TimingHandler(bbctrl.APIHandler):
     """Return the bbctrl process startup timeline as JSON.
 
@@ -992,6 +1012,10 @@ class Web(tornado.web.Application):
             (r'/api/time', TimeHandler),
             (r'/api/rotary', RotaryHandler),
             (r'/api/remote-diagnostics', RemoteDiagnosticsHandler),
+            (r'/api/hooks', HooksGetHandler),
+            (r'/api/hooks/save', HooksSaveHandler),
+            (r'/api/hooks/status', HooksStatusHandler),
+            (r'/api/hooks/fire/([\w-]+)', HooksFireHandler),
             (r'/(.*)', StaticFileHandler,
              {'path': bbctrl.get_resource('http/'),
               'default_filename': 'index.html'}),