Add automatic versioned releases

[tdecroyere]

Add the first Elemental automatic release pipeline while reusing the existing build/test/package mechanics.

Versioning

• add version.cmake as the semantic version/stage source (1.0.0, dev)
• resolve prerelease build numbers from the highest existing numeric release tag, so the normalized historical dev.1…dev.5 sequence naturally continues at dev.6
• keep the build counter monotonic across dev, alpha, beta, and rc
• fail if the resolved tag already exists instead of moving/reusing release identity
• require .github/release-notes/<version>.md before a stable release can proceed

Build / CI topology

• keep Build CI as the required pull-request build/test workflow
• stop running that same matrix separately on pushes to main
• add an optional build_number input to the existing reusable build.yml
• inject the resolved version into the existing public header inside each ephemeral build checkout before configure/build/install
• preserve the current cmake --install staging and archive layout
• validate release-version resolution and prerelease-note generation on pull requests without publishing

Releases

• add a serialized Release workflow for pushes to main
• run the existing build/test matrix once and reuse its artifacts for release publication
• publish Elemental, ElementalTools, and sample binary archives as durable GitHub Release assets; test archives remain CI-only
• create v<version> on the exact main SHA
• mark dev / alpha / beta / rc releases as prereleases

Release notes

• adapt the WoW Stream Overlay PR-body/direct-commit release-note generator to Elemental and beta
• same-stage prereleases describe changes since the previous release
• stage transitions summarize the broader release cycle since the latest stable tag
• stable releases use the versioned editorial file from .github/release-notes/<version>.md

Validation

• Build CI #480: Windows x64, macOS arm64, Linux x64 build/install/package/tests all passed after the cross-platform version-injection fix
• Build CI #482 on current head: all build/test jobs passed
• validate-release resolves the next version as 1.0.0-dev.6 and generates the prerelease notes preview successfully
• CI caught and fixed a Windows CRLF issue in the header rewrite and a PowerShell-native-command issue in the release-tag existence probe

Sample asset versioning remains intentionally out of scope. This PR only makes the already-built binary/sample packages durable release assets.

Do not merge without Thomas's explicit approval.