docs(project): add README, CI workflow, migration guide, and fix asset docs

- README.md: player-facing install, controls, features, and test instructions
- .github/workflows/ci.yml: clippy + headless tests + release build on push/PR
- solitaire_server/migrations/README.md: naming convention and workflow for
  adding future schema migrations
- ARCHITECTURE.md §14: rewrite Asset Pipeline to reflect procedural rendering
  (no image files used; audio only, embedded via include_bytes!)
- ARCHITECTURE.md §2 / §13: fix workspace structure and audio file listing
- CLAUDE.md: clarify asset embedding rule (audio only; visuals are procedural)
- server_tests.rs: add auth_rate_limit_returns_429_on_11th_request test using
  build_router() (rate limiting ON) to verify the GovernorLayer is wired correctly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,82 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+env:
+  CARGO_TERM_COLOR: always
+  RUSTFLAGS: "-D warnings"
+
+jobs:
+  test:
+    name: Test & Lint
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust stable
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+
+      - name: Install Linux audio/display dependencies
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends \
+            libasound2-dev libudev-dev libxkbcommon-dev
+
+      - name: Cache cargo registry and build artifacts
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Clippy (all crates, zero warnings)
+        run: cargo clippy --workspace -- -D warnings
+
+      - name: Test (headless crates only — no display required)
+        run: |
+          cargo test -p solitaire_core
+          cargo test -p solitaire_sync
+          cargo test -p solitaire_data
+          cargo test -p solitaire_server
+
+  build:
+    name: Release Build
+    runs-on: ubuntu-latest
+    needs: test
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust stable
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Install Linux audio/display dependencies
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends \
+            libasound2-dev libudev-dev libxkbcommon-dev
+
+      - name: Cache cargo registry and build artifacts
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-release-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-release-
+
+      - name: Build release binaries
+        run: cargo build --workspace --release