🏗️ Refactor: Major LLVM codegen modularization + Phase 15 docs cleanup + Phase 21 DDD concept

## LLVM Codegen Refactoring (by ChatGPT5)
- Split massive boxcall.rs into focused submodules:
  - strings.rs: String method optimizations (concat, length)
  - arrays.rs: Array operations (get, set, push, length)
  - maps.rs: Map operations (get, set, has, size)
  - fields.rs: getField/setField handling
  - invoke.rs: Tagged invoke implementation
  - marshal.rs: Helper functions for marshaling
- Improved code organization and maintainability
- No functional changes, pure refactoring

## Phase 15 Documentation Cleanup
- Restructured phase-15 folder:
  - implementation/: Technical implementation docs
  - planning/: Planning and sequence docs
  - archive/: Redundant/old content
- Removed duplicate content (80k→20k line reduction mentioned 5 times)
- Converted all .txt files to .md for consistency
- Fixed broken links in README.md
- Removed redundant INDEX.md

## Phase 21: Database-Driven Development (New)
- Revolutionary concept: Source code in SQLite instead of files
- Instant refactoring with SQL transactions
- Structured management of boxes, methods, dependencies
- Technical design with security considerations
- Vision: World's first DB-driven programming language

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

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

src/backend/llvm/compiler/codegen/instructions/boxcall/fields.rs

@@ -0,0 +1,93 @@
+use std::collections::HashMap;
+
+use inkwell::{values::BasicValueEnum as BVE, AddressSpace};
+
+use crate::backend::llvm::context::CodegenContext;
+use crate::mir::ValueId;
+
+/// Handle getField/setField; returns true if handled.
+pub(super) fn try_handle_field_method<'ctx>(
+    codegen: &CodegenContext<'ctx>,
+    vmap: &mut HashMap<ValueId, inkwell::values::BasicValueEnum<'ctx>>,
+    dst: &Option<ValueId>,
+    method: &str,
+    args: &[ValueId],
+    recv_h: inkwell::values::IntValue<'ctx>,
+) -> Result<bool, String> {
+    let i64t = codegen.context.i64_type();
+    match method {
+        "getField" => {
+            if args.len() != 1 {
+                return Err("getField expects 1 arg (name)".to_string());
+            }
+            let name_v = *vmap.get(&args[0]).ok_or("getField name missing")?;
+            let name_p = if let BVE::PointerValue(pv) = name_v {
+                pv
+            } else {
+                return Err("getField name must be pointer".to_string());
+            };
+            let i8p = codegen.context.ptr_type(AddressSpace::from(0));
+            let fnty = i64t.fn_type(&[i64t.into(), i8p.into()], false);
+            let callee = codegen
+                .module
+                .get_function("nyash.instance.get_field_h")
+                .unwrap_or_else(|| codegen.module.add_function("nyash.instance.get_field_h", fnty, None));
+            let call = codegen
+                .builder
+                .build_call(callee, &[recv_h.into(), name_p.into()], "getField")
+                .map_err(|e| e.to_string())?;
+            if let Some(d) = dst {
+                let rv = call
+                    .try_as_basic_value()
+                    .left()
+                    .ok_or("get_field returned void".to_string())?;
+                let h = if let BVE::IntValue(iv) = rv {
+                    iv
+                } else {
+                    return Err("get_field ret expected i64".to_string());
+                };
+                let pty = codegen.context.ptr_type(AddressSpace::from(0));
+                let ptr = codegen
+                    .builder
+                    .build_int_to_ptr(h, pty, "gf_handle_to_ptr")
+                    .map_err(|e| e.to_string())?;
+                vmap.insert(*d, ptr.into());
+            }
+            Ok(true)
+        }
+        "setField" => {
+            if args.len() != 2 {
+                return Err("setField expects 2 args (name, value)".to_string());
+            }
+            let name_v = *vmap.get(&args[0]).ok_or("setField name missing")?;
+            let val_v = *vmap.get(&args[1]).ok_or("setField value missing")?;
+            let name_p = if let BVE::PointerValue(pv) = name_v {
+                pv
+            } else {
+                return Err("setField name must be pointer".to_string());
+            };
+            let val_h = match val_v {
+                BVE::PointerValue(pv) => codegen
+                    .builder
+                    .build_ptr_to_int(pv, i64t, "valp2i")
+                    .map_err(|e| e.to_string())?,
+                BVE::IntValue(iv) => iv,
+                BVE::FloatValue(_) => return Err("setField value must be int/handle".to_string()),
+                _ => return Err("setField value must be int/handle".to_string()),
+            };
+            let i8p = codegen.context.ptr_type(AddressSpace::from(0));
+            let fnty = i64t.fn_type(&[i64t.into(), i8p.into(), i64t.into()], false);
+            let callee = codegen
+                .module
+                .get_function("nyash.instance.set_field_h")
+                .unwrap_or_else(|| codegen.module.add_function("nyash.instance.set_field_h", fnty, None));
+            let _ = codegen
+                .builder
+                .build_call(callee, &[recv_h.into(), name_p.into(), val_h.into()], "setField")
+                .map_err(|e| e.to_string())?;
+            Ok(true)
+        }
+        _ => Ok(false),
+    }
+}
+