fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

lang/src/shared/common/string_helpers.hako

@@ -25,7 +25,7 @@ static box StringHelpers {
     local i = 0
     local neg = 0
     if s.substring(0,1) == "-" { neg = 1  i = 1 }
-    local n = s.size()
+    local n = s.length()
     if i >= n { return 0 }
     local acc = 0
     loop (i < n) {
@@ -46,7 +46,7 @@ static box StringHelpers {
     if s == null { return "\"\"" }
     local out = ""
     local i = 0
-    local n = s.size()
+    local n = s.length()
     loop (i < n) {
       local ch = s.substring(i, i+1)
       if ch == "\\" { out = out + "\\\\" }
@@ -65,7 +65,7 @@ static box StringHelpers {
   // Check if string is numeric-like (optional leading '-', then digits).
   is_numeric_str(s) {
     if s == null { return 0 }
-    local n = s.size()
+    local n = s.length()
     if n == 0 { return 0 }
     local i = 0
     if s.substring(0,1) == "-" { if n == 1 { return 0 } i = 1 }
@@ -95,8 +95,8 @@ static box StringHelpers {
 
   // Pattern matching
   starts_with(src, i, pat) {
-    local n = src.size()
-    local m = pat.size()
+    local n = src.length()
+    local m = pat.length()
     if i + m > n { return 0 }
     local k = 0
     loop(k < m) {
@@ -109,8 +109,8 @@ static box StringHelpers {
   // Keyword match with word boundary (next char not [A-Za-z0-9_])
   starts_with_kw(src, i, kw) {
     if me.starts_with(src, i, kw) == 0 { return 0 }
-    local n = src.size()
-    local j = i + kw.size()
+    local n = src.length()
+    local j = i + kw.length()
     if j >= n { return 1 }
     local ch = src.substring(j, j+1)
     if me.is_alpha(ch) || me.is_digit(ch) { return 0 }
@@ -119,8 +119,8 @@ static box StringHelpers {
 
   // String search
   index_of(src, i, pat) {
-    local n = src.size()
-    local m = pat.size()
+    local n = src.length()
+    local m = pat.length()
     if m == 0 { return i }
     local j = i
     loop(j + m <= n) {
@@ -133,7 +133,7 @@ static box StringHelpers {
   // Trim spaces and tabs (with optional semicolon at end)
   trim(s) {
     local i = 0
-    local n = s.size()
+    local n = s.length()
     loop(i < n && (s.substring(i,i+1) == " " || s.substring(i,i+1) == "\t")) { i = i + 1 }
     local j = n
     loop(j > i && (s.substring(j-1,j) == " " || s.substring(j-1,j) == "\t" || s.substring(j-1,j) == ";")) { j = j - 1 }
@@ -143,7 +143,7 @@ static box StringHelpers {
   // Skip whitespace from position i
   skip_ws(src, i) {
     if src == null { return i }
-    local n = src.size()
+    local n = src.length()
     local cont = 1
     local guard = 0
     local max = 100000
@@ -160,8 +160,8 @@ static box StringHelpers {
   last_index_of(src, pat) {
     if src == null { return -1 }
     if pat == null { return -1 }
-    local n = src.size()
-    local m = pat.size()
+    local n = src.length()
+    local m = pat.length()
     if m == 0 { return n }
     if m > n { return -1 }
     local i = n - m