feat: complete M0.1-M0.4 phases

M0.1 - Cargo workspace + crate skeletons
  - 6-crate workspace with correct dependency direction
  - CI/CD pipeline with GitHub Actions
  - Integration tests verifying build and dependency structure

M0.2 - Domain types and sha256 identity
  - Level (L0, L1, L2) enum with proper serde formatting
  - Role enum (User, Assistant, ToolResult, System)
  - Record, Chunk, and MemoryNode domain types
  - Content-hash identity system ensuring rebuild idempotence
  - Newtypes (ProjectId, QueryId, RunId) with validation
  - Round-trip serde tests for all types

M0.3 - RecordSource trait + ChunkPolicy
  - RecordSource trait for streaming record sources
  - Chunk policy with token budgets and boundary modes
  - TokenCounter trait with CharsOverFourCounter stub
  - Chunking stream that respects budgets without splitting records
  - VecSource for testing
  - Integration tests verifying lossless chunking and budget adherence

M0.4 - Tokenizer-backed chunk sizing
  - Vendored Qwen2 tokenizer with hash verification
  - QwenTokenCounter implementing proper token counting
  - Hash guard that fails on modified tokenizer
  - mem tokens CLI subcommand for token counting
  - Integration tests with known string counts, hash guards, and budget verification

Total: 19 integration tests passing, all phases verified to compose correctly
Workspace builds cleanly with no clippy warnings

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, develop ]
+  pull_request:
+    branches: [ main, develop ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  build:
+    name: Build and Lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      
+      - name: Build workspace
+        run: cargo build --workspace
+      
+      - name: Run clippy
+        run: cargo clippy --workspace -- -D warnings
+      
+      - name: Run tests
+        run: cargo test --test it_workspace