Wire up reactive signal updates to conditionals

Critical change that makes conditionals reactive:

- Added signal_conditional_deps map to track dependencies
- Added _extract_signals_from_expr() to find signals in expressions
- Populate dependency map during _collect_conditionals()
- Replace TODO comments in signal setters with reevaluate calls

How it works:
1. During collection, analyze if/match test/subject expressions
2. Extract all signal names referenced in conditions
3. Build map: signal_name -> [conditional_ids that use it]
4. When signal is updated (assign/augassign), call reevaluate for each dependent conditional

Example: set_tab_0() now:
  store i32 0, i32* @signal_Tabs_tab_index
  call void @reevaluate_conditional_4()
  call void @reevaluate_conditional_5()
  call void @reevaluate_conditional_6()
  call void @reevaluate_conditional_7()

This makes tabs fully interactive!

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

examples/tabs/Tabs.ll

@@ -121,7 +121,10 @@ entry:
 define void @set_setting_0() {
 entry:
   store i32 0, i32* @signal_VerticalTabs_setting_tab
-  ; TODO: Update DOM nodes bound to setting_tab
+  call void @reevaluate_conditional_0()
+  call void @reevaluate_conditional_1()
+  call void @reevaluate_conditional_2()
+  call void @reevaluate_conditional_3()
   ret void
 }
 
@@ -129,7 +132,10 @@ entry:
 define void @set_setting_1() {
 entry:
   store i32 1, i32* @signal_VerticalTabs_setting_tab
-  ; TODO: Update DOM nodes bound to setting_tab
+  call void @reevaluate_conditional_0()
+  call void @reevaluate_conditional_1()
+  call void @reevaluate_conditional_2()
+  call void @reevaluate_conditional_3()
   ret void
 }
 
@@ -137,7 +143,10 @@ entry:
 define void @set_setting_2() {
 entry:
   store i32 2, i32* @signal_VerticalTabs_setting_tab
-  ; TODO: Update DOM nodes bound to setting_tab
+  call void @reevaluate_conditional_0()
+  call void @reevaluate_conditional_1()
+  call void @reevaluate_conditional_2()
+  call void @reevaluate_conditional_3()
   ret void
 }
 
@@ -609,7 +618,10 @@ entry:
 define void @set_tab_0() {
 entry:
   store i32 0, i32* @signal_Tabs_tab_index
-  ; TODO: Update DOM nodes bound to tab_index
+  call void @reevaluate_conditional_4()
+  call void @reevaluate_conditional_5()
+  call void @reevaluate_conditional_6()
+  call void @reevaluate_conditional_7()
   ret void
 }
 
@@ -617,7 +629,10 @@ entry:
 define void @set_tab_1() {
 entry:
   store i32 1, i32* @signal_Tabs_tab_index
-  ; TODO: Update DOM nodes bound to tab_index
+  call void @reevaluate_conditional_4()
+  call void @reevaluate_conditional_5()
+  call void @reevaluate_conditional_6()
+  call void @reevaluate_conditional_7()
   ret void
 }
 
@@ -625,7 +640,10 @@ entry:
 define void @set_tab_2() {
 entry:
   store i32 2, i32* @signal_Tabs_tab_index
-  ; TODO: Update DOM nodes bound to tab_index
+  call void @reevaluate_conditional_4()
+  call void @reevaluate_conditional_5()
+  call void @reevaluate_conditional_6()
+  call void @reevaluate_conditional_7()
   ret void
 }