Phase 11-12: LLVM backend initial, semantics layer, plugin unification

Major changes:
- LLVM backend initial implementation (compiler.rs, llvm mode)
- Semantics layer integration in interpreter (operators.rs)
- Phase 12 plugin architecture revision (3-layer system)
- Builtin box removal preparation
- MIR instruction set documentation (26→Core-15 migration)
- Cross-backend testing infrastructure
- Await/nowait syntax support

New features:
- LLVM AOT compilation support (--backend llvm)
- Semantics layer for interpreter→VM flow
- Tri-backend smoke tests
- Plugin-only registry mode

Bug fixes:
- Interpreter plugin box arithmetic operations
- Branch test returns incorrect values

Documentation:
- Phase 12 README.md updated with new plugin architecture
- Removed obsolete NYIR proposals
- Added LLVM test programs documentation

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

.github/workflows/llvm-aot-smoke.yml

@@ -0,0 +1,58 @@
+name: LLVM AOT Smoke
+
+on:
+  push:
+    paths:
+      - 'src/**'
+      - 'crates/**'
+      - 'apps/**'
+      - 'tools/**'
+      - 'Cargo.toml'
+      - 'Cargo.lock'
+      - '.github/workflows/llvm-aot-smoke.yml'
+  pull_request:
+    paths:
+      - 'src/**'
+      - 'crates/**'
+      - 'apps/**'
+      - 'tools/**'
+      - 'Cargo.toml'
+      - 'Cargo.lock'
+
+jobs:
+  llvm-aot:
+    runs-on: ubuntu-latest
+    env:
+      CARGO_TERM_COLOR: always
+      NYASH_CLI_VERBOSE: '1'
+      NYASH_DISABLE_PLUGINS: '1'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Rust (stable)
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache cargo registry and build
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Install LLVM 18 (llvm-config-18)
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y curl ca-certificates lsb-release wget gnupg
+          curl -fsSL https://apt.llvm.org/llvm.sh -o llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 18
+          llvm-config-18 --version
+
+      - name: Run LLVM AOT smokes
+        run: bash tools/llvm_smoke.sh
+

.github/workflows/llvm-vinvoke-smoke.yml

@@ -0,0 +1,58 @@
+name: LLVM VInvoke Smoke
+
+on:
+  push:
+    paths:
+      - 'src/**'
+      - 'crates/**'
+      - 'apps/**'
+      - 'tools/**'
+      - 'Cargo.toml'
+      - 'Cargo.lock'
+      - '.github/workflows/llvm-vinvoke-smoke.yml'
+  pull_request:
+    paths:
+      - 'src/**'
+      - 'crates/**'
+      - 'apps/**'
+      - 'tools/**'
+      - 'Cargo.toml'
+      - 'Cargo.lock'
+
+jobs:
+  llvm-vinvoke:
+    runs-on: ubuntu-latest
+    env:
+      CARGO_TERM_COLOR: always
+      NYASH_CLI_VERBOSE: '1'
+      # Plugins enabled (do not set NYASH_DISABLE_PLUGINS)
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Rust (stable)
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache cargo registry and build
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Install LLVM 18 (llvm-config-18)
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y curl ca-certificates lsb-release wget gnupg build-essential libzstd-dev
+          curl -fsSL https://apt.llvm.org/llvm.sh -o llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 18
+          llvm-config-18 --version
+
+      - name: Run LLVM VInvoke + Array smoke tests
+        run: |
+          NYASH_LLVM_VINVOKE_RET_SMOKE=1 NYASH_LLVM_ARRAY_RET_SMOKE=1 ./tools/llvm_smoke.sh release