Engine: trigger filter support, sx-on event mapping, JS inline handlers

1. parse-trigger-spec: strip [condition] from event names, store as
   "filter" modifier (e.g. keyup[key=='s'] → event="keyup", filter=...)
2. bind-event: evaluate filter conditions via JS Function constructor
   when filter modifier is present
3. bind-inline-handlers: map afterSwap/beforeRequest etc. to sx:*
   event names (matching what the engine dispatches)
4. bind-inline-handlers: detect JS syntax in body (contains ".") and
   eval via Function instead of SX parse — enables this.reset() etc.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/engine.sx

@@ -63,7 +63,26 @@
                             (starts-with? tok "from:")
                             (dict-set! mods "from" (slice tok 5))))
                         (rest tokens))
-                      (dict "event" (first tokens) "modifiers" mods))))))
+                      (let
+                        ((raw-event (first tokens)))
+                        (let
+                          ((bracket-idx (index-of raw-event "[")))
+                          (if
+                            (>= bracket-idx 0)
+                            (do
+                              (dict-set!
+                                mods
+                                "filter"
+                                (slice
+                                  raw-event
+                                  (+ bracket-idx 1)
+                                  (- (len raw-event) 1)))
+                              (dict
+                                "event"
+                                (slice raw-event 0 bracket-idx)
+                                "modifiers"
+                                mods))
+                            (dict "event" raw-event "modifiers" mods)))))))))
             raw-parts))))))
 
 (define