refactor: Quick Win cleanup - 102 lines deleted, zero regressions

Completed three high-efficiency refactoring tasks:

## Task 1: Pattern1Context deletion (40 lines)
- Removed deprecated Pattern1Context struct from simple_while_minimal.rs
- Removed context parameter from lowering pipeline
- Simplified API surface (one less unused type)
- Files: simple_while_minimal.rs, pattern1_minimal.rs, loop_to_join.rs

## Task 2: #[allow(dead_code)] cleanup (62 lines)
- Deleted new_with_outputs() from inline_boundary.rs (truly dead, deprecated)
- Deleted extract_type_hint() from generic_type_resolver.rs (future placeholder)
- Removed 3 incorrect annotations (code IS actually used)
- Added clear comments for future-work items

## Task 3: Test organization (0 lines, +26 doc lines)
- Added 4-section navigation to loop_scope_shape/tests.rs
- Improved test discoverability (17 tests → organized by module)
- Low-risk organization improvement
- Easy path for future per-module test file splitting

## Summary
- Total deletion: 102 net lines
- Files modified: 9
- Build status: ✅ Clean (0 errors, 0 warnings)
- Test status: ✅ 21/21 PASS
- Regressions: 0

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

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

src/mir/join_ir/lowering/loop_scope_shape/shape.rs

@@ -57,7 +57,6 @@ impl LoopVarClass {
 /// - `progress_carrier`: 進捗チェック用（将来の Verifier で使用予定）
 /// - `variable_definitions`: definition blocks collected from LoopFormIntake snapshots
 #[derive(Debug, Clone)]
-#[allow(dead_code)] // Block IDs and progress_carrier are reserved for future F-3/F-4 use
 pub(crate) struct LoopScopeShape {
     pub header: BasicBlockId,
     pub body: BasicBlockId,

src/mir/join_ir/lowering/loop_scope_shape/tests.rs

@@ -1,9 +1,25 @@
+//! Tests for loop_scope_shape module
+//!
+//! ## Test Organization
+//!
+//! This file contains tests for multiple components:
+//! - **LoopScopeShape tests** (shape.rs): from_loop_form, needs_phi, block_ids, ordering
+//! - **CaseAContext tests** (case_a*.rs): validation, lowering shape
+//! - **Variable classification tests** (structural.rs): classify, phi consistency
+//! - **Variable definitions tests** (builder.rs): availability, inspector
+//!
+//! Future work: Consider splitting into per-module test files for better organization.
+
 use super::shape::LoopVarClass;
 use super::*;
 use crate::mir::join_ir::lowering::loop_form_intake::LoopFormIntake;
 use crate::mir::{BasicBlockId, MirQuery, ValueId};
 use std::collections::{BTreeMap, BTreeSet};
 
+// ============================================================================
+// Test Fixtures (shared across all tests)
+// ============================================================================
+
 fn make_dummy_loop_form() -> crate::mir::loop_form::LoopForm {
     crate::mir::loop_form::LoopForm {
         preheader: BasicBlockId::new(1),
@@ -47,6 +63,10 @@ impl MirQuery for EmptyQuery {
     }
 }
 
+// ============================================================================
+// LoopScopeShape Tests (shape.rs)
+// ============================================================================
+
 #[test]
 fn test_from_loop_form_basic() {
     let loop_form = make_dummy_loop_form();
@@ -118,6 +138,10 @@ fn test_ordered_accessors() {
     assert!(carriers.contains(&"i".to_string()));
 }
 
+// ============================================================================
+// CaseAContext Tests (case_a*.rs)
+// ============================================================================
+
 /// CaseAContext::from_scope で header == exit のとき None を返すテスト
 #[test]
 fn test_from_scope_validation_header_eq_exit() {
@@ -234,6 +258,10 @@ fn test_needs_phi_consistency() {
     }
 }
 
+// ============================================================================
+// Variable Classification Tests (structural.rs)
+// ============================================================================
+
 /// classify() メソッドのテスト
 #[test]
 fn test_classify_method() {
@@ -326,6 +354,10 @@ fn test_get_exit_live() {
     assert!(exit_live.contains("i"));
 }
 
+// ============================================================================
+// Variable Definitions Tests (builder.rs)
+// ============================================================================
+
 /// Phase 48-4: is_available_in_all() API テスト（空の variable_definitions）
 #[test]
 fn test_is_available_in_all_phase48_4() {