feat: Add support for action modifier keys like ctrl,shift,alt.

docs/DEVPLAN.md

@@ -349,7 +349,14 @@ navigate directories without spawning new processes.
   pass `-la` to it. The output would include both the
   selected item and the user-supplied arguments.
 
-  Open questions:
+  **Partially resolved:** modifier key support has landed.
+  Structured output and hook events now carry a `modifiers`
+  field when shift/ctrl/alt are held during confirmation.
+  This covers the signaling side: scripts can detect
+  Shift+Enter and branch on it. The free-text argument
+  input (where does the user type `-la`?) is still open.
+
+  Remaining open questions:
   - UX flow: does the filter text become the args on
     Shift+Enter? Or does Shift+Enter open a second input
     field for args after selection? The filter-as-args
@@ -363,9 +370,6 @@ navigate directories without spawning new processes.
     matches exactly one item just confirm that item (current
     behaviour), or should it also treat any "extra" text
     as args? Probably not, too implicit.
-  - Keybind: Shift+Enter is natural, but some terminals
-    don't distinguish it from Enter. May need a fallback
-    like Ctrl+Enter or a normal-mode keybind.
 
   This is a core feature (new keybind, new output field),
   not just a launcher script concern. Fits naturally after