feat: Expand hook system to handle simple exec and plugin extensibility.

Item Model Expansion - Item now caches sublabel, icon, group with accessors. Added resolve_field_path() for dotted path traversal and field_value() on Item.
Output Struct - New OutputItem with OutputAction (select/cancel) and index. Object values flatten, strings get a value field. MenuResult::Selected now carries { value, index }.
Hook Types - Replaced the old Hook trait with HookEvent (serializable, 6 variants), HookResponse (deserializable, 5 commands), HookHandler trait (sync for dyn-compatibility), and parse_hook_response() with tracing warnings.
New Actions & Menu Methods - Added ReplaceItems, RemoveItems, ProcessHookResponse, CloseMenu actions. Menu trait gained original_index(), replace_all(), remove_by_indices(), formatted_label(). Pipeline got rebuild() and rebuild_with_values(). Smart cursor preservation on replace.
Lifecycle Events - MenuRunner emits Open, Close, Hover, Select, Cancel, Filter events through the dispatcher. Cursor tracking for Hover detection.
Debounce - DebouncedDispatcher with 4 modes: None, Debounce, CancelStale, DebounceAndCancelStale. Defaults: hover=DebounceAndCancelStale(200ms), filter=Debounce(200ms).
Exec Hooks - ShellExecHandler maps --on-{open,close,hover,select,cancel,filter}-exec flags to fire-and-forget subprocesses. Event JSON piped to stdin.
Handler Hooks - ShellHandlerHook launches persistent processes per --on-{event} flag. Bidirectional JSON lines: events on stdin, responses on stdout flowing back through Action::ProcessHookResponse. CompositeHookHandler dispatches to both.
--filter-fields - --filter-fields label,sublabel,meta.tags searches multiple fields. Combined text for fuzzy, individual for exact/regex.
--format - FormatTemplate parses {field.path} placeholders. --format '{label} - {sublabel}' controls display. TUI renders formatted_text when available.
Field Filters - meta.res:3840 in query syntax matches specific fields. !meta.res:3840 for inverse. Pipeline stores item Values for field resolution. Requires dotted path (single word colons stay fuzzy).

crates/pikl-tui/src/lib.rs

@@ -194,7 +194,8 @@ fn render_menu(frame: &mut ratatui::Frame, vs: &ViewState, filter_text: &str) {
             } else {
                 Style::default()
             };
-            ListItem::new(vi.label.as_str()).style(style)
+            let text = vi.formatted_text.as_deref().unwrap_or(vi.label.as_str());
+            ListItem::new(text).style(style)
         })
         .collect();
 
@@ -318,14 +319,17 @@ mod tests {
             visible_items: vec![
                 VisibleItem {
                     label: "alpha".into(),
+                    formatted_text: None,
                     index: 0,
                 },
                 VisibleItem {
                     label: "bravo".into(),
+                    formatted_text: None,
                     index: 1,
                 },
                 VisibleItem {
                     label: "charlie".into(),
+                    formatted_text: None,
                     index: 2,
                 },
             ],