fix: publish ARM64 local-mode wheels

[abhinavkr26104]

Summary

• add Linux ARM64 and Windows ARM64 wheel targets to the publish matrix
• map those targets to the SEA asset names already produced by the release pipeline
• add resolver tests for x64 and ARM64 filenames on Linux and Windows

The packaging jobs only download and bundle architecture-specific assets, so the existing hosted x64 runners can produce these pure-Python platform-tagged wheels without executing the bundled binary.

Testing

• uv run --frozen pytest tests/test_sea_binary.py -q (8 passed)
• uv run --frozen ruff check .
• uv run --frozen pyright -p .
• uv run --frozen mypy --platform linux .
• full Python 3.9 and 3.14 suites run on Windows; only the pre-existing Windows failures addressed by Make byte fixtures checkout-stable and run tests on Windows CI #355 remained

Fixes #352

---

Summary by cubic

Publishes ARM64 wheels for Linux and Windows in local mode. Previously we only shipped x64 wheels; now we also build manylinux2014_aarch64 and win_arm64 to enable ARM64 installs without source builds.

• Map new matrix entries to existing SEA assets: stagehand-server-v3-linux-arm64 and stagehand-server-v3-win32-arm64.exe.
• Add tests that assert default binary filenames for Linux and Windows on x64 and ARM64.
• Use hosted x64 runners only; packaging downloads architecture-specific assets and does not execute them. No runtime behavior change.

^{Written for commit 5f95115. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

Architecture diagram

sequenceDiagram
    participant Pub as publish-pypi.yml
    participant GH as GitHub Actions Matrix
    participant DL as download-binary.py
    participant PKG as Packaging (wheel build)
    participant PYPI as PyPI
    participant CLI as Client Install/Resolve
    participant SEA as stagehand/_sea/binary resolution

    Note over Pub,PYPI: NEW: ARM64 Wheel Build & Publish Pipeline

    Pub->>GH: Define wheel targets (x64 + NEW: ARM64)
    GH->>GH: Iterate matrix entries (linux-x64, linux-arm64, macos, win-x64, win-arm64)
    
    loop Each matrix entry
        GH->>GH: runs-on hosted x64 runner (any OS)
        GH->>DL: download binary (binary_name)
        
        alt NEW: ARM64 targets
            DL-->>GH: stagehand-linux-arm64 OR stagehand-win32-arm64.exe
        else Existing x64
            DL-->>GH: stagehand-linux-x64 OR stagehand-win32-x64.exe
        end
        
        GH->>PKG: Place binary in src/stagehand/_sea/
        PKG->>PKG: Set wheel_platform_tag (manylinux2014_aarch64 / win_arm64)
        PKG->>PKG: Build pure-Python wheel (binary not executed)
        PKG->>PYPI: Publish platform-tagged wheel
    end

    Note over CLI,SEA: Runtime Resolution (unchanged logic, NEW: filenames)

    CLI->>SEA: Resolve binary for current platform
    SEA->>SEA: Determine sys.platform + machine
    
    alt linux + aarch64
        SEA->>SEA: default_binary_filename() = stagehand-linux-arm64
    else linux + x86_64
        SEA->>SEA: default_binary_filename() = stagehand-linux-x64
    else win32 + ARM64
        SEA->>SEA: default_binary_filename() = stagehand-win32-arm64.exe
    else win32 + AMD64
        SEA->>SEA: default_binary_filename() = stagehand-win32-x64.exe
    end
    
    SEA->>PYPI: Fetch matching platform-tagged wheel
    PYPI-->>SEA: Wheel with bundled SEA binary
    SEA-->>CLI: Ready for use

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_{Re-trigger cubic}