feat(llvm/phi): Phase 277 P1 - fail-fast validation for PHI strict mode

## Summary
Implemented fail-fast validation for PHI ordering and value resolution in strict mode.

## Changes

### P1-1: Strict mode for "PHI after terminator"
- File: `src/llvm_py/phi_wiring/wiring.py::ensure_phi`
- Behavior: `NYASH_LLVM_PHI_STRICT=1` → RuntimeError if PHI created after terminator
- Default: Warning only (no regression)

### P1-2: Strict mode for "fallback 0"
- File: `src/llvm_py/phi_wiring/wiring.py::wire_incomings`
- Behavior: Strict mode forbids silent fallback to 0 (2 locations)
  - Location 1: Unresolvable incoming value
  - Location 2: Type coercion failure
- Error messages point to next debug file: `llvm_builder.py::_value_at_end_i64`

### P1-3: Connect verify_phi_ordering() to execution path
- File: `src/llvm_py/builders/function_lower.py`
- Behavior: Verify PHI ordering after all instructions emitted
- Debug mode: Shows "✅ All N blocks have correct PHI ordering"
- Strict mode: Raises RuntimeError with block list if violations found

## Testing
✅ Test 1: strict=OFF - passes without errors
✅ Test 2: strict=ON - passes without errors (no violations in test fixtures)
✅ Test 3: debug mode - verify_phi_ordering() connected and running

## Scope
- LLVM harness (Python) changes only
- No new environment variables (uses existing 3 from Phase 277 P2)
- No JoinIR/Rust changes (root fix is Phase 279)
- Default behavior unchanged (strict mode opt-in)

## Next Steps
- Phase 278: Remove deprecated env var support
- Phase 279: Root fix - unify "2本のコンパイラ" pipelines

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/reference/language/quick-reference.md

@@ -40,21 +40,18 @@ Semicolons and ASI (Automatic Semicolon Insertion)
   - Ambiguous continuations; parser must Fail‑Fast with a clear message.
 
 Truthiness (boolean context)
-- `Bool` → itself
-- `Integer` → `0` is false; non‑zero is true
-- `String` → empty string is false; otherwise true
-- `Array`/`Map` → non‑null is true (size is not consulted)
-- `null`/`void` → false
+- SSOT: `reference/language/types.md`（runtime truthiness）
+- 実行上は `Bool/Integer/Float/String/Void` が中心。`BoxRef` は一部のコアBoxのみ許可され、その他は `TypeError`（Fail-Fast）。
 
 Equality and Comparison
-- `==` and `!=` compare primitive values (Integer/Bool/String). No implicit cross‑type coercion.
-- Box/Instance comparisons should use explicit methods (`equals`), or be normalized by the builder.
-- Compare operators `< <= > >=` are defined on integers (MVP).
+- SSOT: `reference/language/types.md`（`==`/`!=` と `< <= > >=` の runtime 仕様）
+- `==` は一部の cross-kind（`Integer↔Bool`, `Integer↔Float`）を best-effort で扱う。その他は `false`。
+- `< <= > >=` は `Integer/Float/String` の **同型同士**のみ（異型は `TypeError`）。
 
 String and Numeric `+`
-- If either side is `String`, `+` is string concatenation.
-- If both sides are numeric, `+` is addition.
-- Other mixes are errors (dev: warn; prod: error) — keep it explicit（必要なら `str(x)` を使う）。
+- SSOT: `reference/language/types.md`（runtime `+` 仕様）
+- `Integer+Integer`, `Float+Float` は加算。片側が `String` なら文字列連結（相手は文字列化）。
+- それ以外（例: `Integer+Bool`, `Integer+Float`）は `TypeError`（Fail-Fast）。
 
 Blocks and Control
 - `if (cond) { ... } [else { ... }]`