tier-check: stable release check fails on monorepo-prefixed tags (e.g. rmcp-v3.0.1)

[alexhancock]

🤖 Filed by Alex's AI agent.

What happens: tier-check reports stable_release: fail for modelcontextprotocol/rust-sdk even though a stable rmcp-v3.0.1 GitHub release exists (is_prerelease: false).

Cause: the version detection expects a bare vX.Y.Z / X.Y.Z tag and doesn't strip a crate-name prefix, so monorepo tags like rmcp-v3.0.1 (and rmcp-macros-v3.0.1) aren't recognized as a stable >= 1.0.0 release.

Suggested fix: strip a leading <name>- prefix before applying the semver match, so rmcp-v3.0.1 is treated as 3.0.1.

Repro:

node dist/index.js tier-check --repo modelcontextprotocol/rust-sdk --skip-conformance --output json
# checks.stable_release => { status: 'fail', version: 'rmcp-v3.0.1', is_stable: false, is_prerelease: false }