feat: Phase 10 reorganization + GC switchable runtime + VM improvements

## 📚 Documentation Updates
- Phase 10 reorganized with comprehensive README
  - Cranelift JIT as main implementation
  - NEW: Phase 10.4 GC Switchable Runtime (world's first\!)
  - Phase 10.5 Self-hosting (parallel)
  - Application migration tests
- Phase 11 created for LLVM AOT research (deferred)
  - Moved phase10_aot_scaffolding.md → Phase 11
  - Moved phase_10_x_llvm_backend_skeleton.md → Phase 11
- Master roadmap updated with GC runtime feature
- Ideas: GC switchable language concept documented

## 🚀 VM Implementation Progress (by ChatGPT5)
- src/backend/vm.rs: Enhanced VM execution
- src/backend/vm_instructions.rs: Instruction improvements
- src/runtime/type_meta.rs: NEW - Type metadata system
- src/boxes/buffer/mod.rs: Buffer optimizations
- src/runtime/mod.rs & plugin_ffi_common.rs: Runtime enhancements

## 🌟 Revolutionary Feature: GC Switchable Runtime
- Development mode: GC on (convenience)
- Production mode: GC off (performance)
- Technical feasibility confirmed by Codex GPT-5
- Implementation plan: After Cranelift JIT

## 📋 Phase 10 Structure
Phase 10.0: Cranelift JIT foundation
Phase 10.1-10.3: JIT implementation & optimization
Phase 10.4: GC Switchable Runtime ← NEW\!
Phase 10.5: Self-hosting (String/Array/Map in Nyash)
Phase 10.9: Application migration tests

🤖 ChatGPT5 says: Ready for Phase 10\! どきどきにゃ！

src/backend/vm.rs

@@ -212,6 +212,8 @@ pub struct VM {
     pub(super) boxcall_pic_hits: std::collections::HashMap<String, u32>,
     /// Mono-PIC: cached direct targets (currently InstanceBox function name)
     pub(super) boxcall_pic_funcname: std::collections::HashMap<String, String>,
+    /// Poly-PIC: per call-site up to 4 entries of (label, version, func_name)
+    pub(super) boxcall_poly_pic: std::collections::HashMap<String, Vec<(String, u32, String)>>,
     /// VTable-like cache: (type, method_id, arity) → direct target (InstanceBox method)
     pub(super) boxcall_vtable_funcname: std::collections::HashMap<String, String>,
     /// Version map for cache invalidation: label -> version
@@ -278,6 +280,7 @@ impl VM {
             exec_start: None,
             boxcall_pic_hits: std::collections::HashMap::new(),
             boxcall_pic_funcname: std::collections::HashMap::new(),
+            boxcall_poly_pic: std::collections::HashMap::new(),
             boxcall_vtable_funcname: std::collections::HashMap::new(),
             type_versions: std::collections::HashMap::new(),
             // TODO: Re-enable when interpreter refactoring is complete
@@ -307,6 +310,7 @@ impl VM {
             exec_start: None,
             boxcall_pic_hits: std::collections::HashMap::new(),
             boxcall_pic_funcname: std::collections::HashMap::new(),
+            boxcall_poly_pic: std::collections::HashMap::new(),
             boxcall_vtable_funcname: std::collections::HashMap::new(),
             type_versions: std::collections::HashMap::new(),
         }
@@ -339,6 +343,10 @@ impl VM {
     pub fn execute_module(&mut self, module: &MirModule) -> Result<Box<dyn NyashBox>, VMError> {
         // Store module for nested calls
         self.module = Some(module.clone());
+        // Optional: dump registry for debugging
+        if std::env::var("NYASH_REG_DUMP").ok().as_deref() == Some("1") {
+            crate::runtime::type_meta::dump_registry();
+        }
         // Reset stats
         self.instr_counter.clear();
         self.exec_start = Some(Instant::now());
@@ -352,10 +360,34 @@ impl VM {
         // Optional: print VM stats
         self.maybe_print_stats();
 
+        // Optional: print cache stats summary
+        if std::env::var("NYASH_VM_PIC_STATS").ok().as_deref() == Some("1") {
+            self.print_cache_stats_summary();
+        }
+
         // Convert result to NyashBox
         Ok(result.to_nyash_box())
     }
 
+    fn print_cache_stats_summary(&self) {
+        let sites_poly = self.boxcall_poly_pic.len();
+        let entries_poly: usize = self.boxcall_poly_pic.values().map(|v| v.len()).sum();
+        let avg_entries = if sites_poly > 0 { (entries_poly as f64) / (sites_poly as f64) } else { 0.0 };
+        let sites_mono = self.boxcall_pic_funcname.len();
+        let hits_total: u64 = self.boxcall_pic_hits.values().map(|v| *v as u64).sum();
+        let vt_entries = self.boxcall_vtable_funcname.len();
+        eprintln!(
+            "[VM] PIC/VT summary: poly_sites={} avg_entries={:.2} mono_sites={} hits_total={} vt_entries={}",
+            sites_poly, avg_entries, sites_mono, hits_total, vt_entries
+        );
+        // Top sites by hits (up to 5)
+        let mut hits: Vec<(&String, &u32)> = self.boxcall_pic_hits.iter().collect();
+        hits.sort_by(|a, b| b.1.cmp(a.1));
+        for (i, (k, v)) in hits.into_iter().take(5).enumerate() {
+            eprintln!("  #{} {} hits={}", i+1, k, v);
+        }
+    }
+
     /// Call a MIR function by name with VMValue arguments
     pub(super) fn call_function_by_name(&mut self, func_name: &str, args: Vec<VMValue>) -> Result<VMValue, VMError> {
         let module_ref = self.module.as_ref().ok_or_else(|| VMError::InvalidInstruction("No active module".to_string()))?;