ci: sync workflows with rules-template

[wep21]

Sync .github/workflows and release packaging with bazel-contrib/rules-template.

• tag.yaml: skip smlx/ccv itself when a tag was cut within 2 weeks. Previously ccv still pushed the tag and only the release job was skipped, leaving a tag without a release.
• release.yaml: bump release_ruleset.yaml to v7.7.0, create the release as a draft and publish it in a finalize job after BCR publish (immutable releases flow).
• release_prep.sh: drop the WORKSPACE / Bazel 6 instructions from release notes.
• .gitattributes: exclude examples/ from the release archive.
• conventional-commits.yaml: add PR title check for ccv.
• actions/checkout: pin to v7.0.1.
• ci.yaml: replace bazel.yaml@v7 with an inline setup-bazel matrix (Bazel 7.x/8.x/9.x × root/examples), remove unused ci.bazelrc, add .bazelignore for examples/.

Built root and examples locally with Bazel 7.x, 8.x and 9.x, and dry-ran release_prep.sh against a local tag.

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