fix(tier-check): extract semver from monorepo release tags, add --tag-prefix

[hashemix]

Description:

tier-check's stable-release check fails for any SDK monorepo that publishes per-package releases.

Two flaws:
1- it picks the first non-draft release regardless of which package it belongs to
2- tag_name.replace(/^v/, '') can only parse plain vX.Y.Z tags and fails on package prefixes.

This PR fixes both by extracting semver from anywhere in the tag and adding --tag-prefix to scope release detection to a single package's tag line. Applied to both stable-release and spec-tracking checks.

Motivation and Context

Closes #151

Our monorepo (rust-mcp-stack/rust-mcp-sdk) uses release-please per-crate tags (rust-mcp-sdk-v1.0.1, rust-mcp-transport-v1.0.0). tier-check is not able to parse the right release tag, because parseInt("rust-mcp-sdk-v1.0.1") → NaN → is_stable = false.

The mcp-use monorepo in #151 hits the sibling problem: the first release in API order belongs to a different package/canary line (mcp-use@1.18.0-canary.3 instead of python-v1.5.2).

How Has This Been Tested?

• npm test - all tests pass (22 new vitest cases in release.test.ts)
• npm run lint - clean
• npm run typecheck - clean
• npm run build - clean
• End-to-end: tier-check --repo rust-mcp-stack/rust-mcp-sdk --skip-conformance now shows ✓ Stable Release 1.0.0 (was ✗ Stable Release rust-mcp-transport-v1.0.0)

Breaking Changes

None for single-package repos with plain v1.2.3 tags — behavior is unchanged. Monorepos now need --tag-prefix to scope to the right package, but without it they graduate from "always fails" to "picks the first parseable semver tag."

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

N/A