feat(joinir): Phase 171-fix ConditionEnv/ConditionBinding architecture

Proper HOST↔JoinIR ValueId separation for condition variables:

- Add ConditionEnv struct (name → JoinIR-local ValueId mapping)
- Add ConditionBinding struct (HOST/JoinIR ValueId pairs)
- Modify condition_to_joinir to use ConditionEnv instead of builder.variable_map
- Update Pattern2 lowerer to build ConditionEnv and ConditionBindings
- Extend JoinInlineBoundary with condition_bindings field
- Update BoundaryInjector to inject Copy instructions for condition variables

This fixes the undefined ValueId errors where HOST ValueIds were being
used directly in JoinIR instructions. Programs now execute (RC: 0),
though loop variable exit values still need Phase 172 work.

Key invariants established:
1. JoinIR uses ONLY JoinIR-local ValueIds
2. HOST↔JoinIR bridging is ONLY through JoinInlineBoundary
3. condition_to_joinir NEVER accesses builder.variable_map

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

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

tools/selfhost/json_parser_string_min.hako

@@ -0,0 +1,54 @@
+// Phase 166: JsonParserBox 単体テスト - String parsing
+// Goal: Validate JsonParserBox can parse simple JSON strings through JoinIR
+
+using "tools/hako_shared/json_parser.hako" with JsonParserBox
+
+static box Main {
+  main(args) {
+    print("=== JsonParserBox String Parsing Tests ===")
+
+    // Test 1: Simple string
+    print("Test 1: Simple string")
+    local json1 = "\"hello\""
+    local result1 = JsonParserBox.parse(json1)
+    if result1 == null {
+      print("  FAIL: parse returned null")
+      return 1
+    }
+    if result1 == "hello" {
+      print("  PASS: got 'hello'")
+    } else {
+      print("  FAIL: expected 'hello', got different value")
+      return 1
+    }
+
+    // Test 2: String with escape sequences
+    print("Test 2: String with escapes (\\n, \\t)")
+    local json2 = "\"line1\\nline2\""
+    local result2 = JsonParserBox.parse(json2)
+    if result2 == null {
+      print("  FAIL: parse returned null")
+      return 1
+    }
+    // Result should contain newline
+    print("  PASS: escape sequences parsed")
+
+    // Test 3: Empty string
+    print("Test 3: Empty string")
+    local json3 = "\"\""
+    local result3 = JsonParserBox.parse(json3)
+    if result3 == null {
+      print("  FAIL: parse returned null")
+      return 1
+    }
+    if result3 == "" {
+      print("  PASS: got empty string")
+    } else {
+      print("  FAIL: expected empty string")
+      return 1
+    }
+
+    print("=== All String Tests PASSED ===")
+    return 0
+  }
+}