Release 1.20.0

Release manifest 1.2.0 (roadmap WS-P task 7; openvibe-contracts 0.60.0, ADR-016 amendment 2).

• createRelease({ clientGeneration, minClientGeneration, shell }) serves client_generation, min_client_generation (also env MIN_CLIENT_GENERATION) and shell: { version, components }, where the version is the first 12 hex of SHA-256 over the named components' ids and versions.
• The meta tag carries data-generation.
• A tab below the minimum generation reloads when safe (required). A changed shell is never applied in place; it prompts.
• release-watch stays under its 5 KB brotli budget (4.94 KB) with a tighter header comment.

The Contracts devDependency moves to 0.60.0.