Harden release and documentation sanitization

[GGULBAE]

Summary

• replace suffix-based npm attestation URL matching with strict URL parsing and exact decoded package@version identity
• reject wrong origin, userinfo, query/fragment, malformed encoding, double encoding, and prefixed identities without throwing
• replace multi-character Markdown heading tag removal with a state machine that cannot synthesize a new tag opener
• add scoped-package and adversarial heading/URL regression coverage

Why

This removes the actual fail-open behavior behind the repository's two open high-severity CodeQL alerts instead of dismissing them as false positives.

Verification

• VITEST_MAX_WORKERS=2 pnpm verify: 59 files / 546 tests
• coverage: 94.08% statements, 86.12% branches, 98.40% functions, 94.56% lines
• pnpm example:typecheck
• focused release/docs semantic tests: pass
• independent adversarial reviews: approve, no P0/P1