chore(release): bump framework and skills version to v2.1.0

- Bump all 8 SKILL.md frontmatter version fields to 2.1.0
- Add v2.1.0 changelog in VERSIONS.md highlighting 2xK grid layout engine (B-20), explicit --agent standardization, and --herdr-session option hardening
- Update skills version matrix in VERSIONS.md

.agents/skills/multi-agent-mux-delegate-job/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: multi-agent-mux-delegate-job
 description: "Delegate a unit of work to any autonomous agent (claude-code, hermes, agy, cline, codex, or a human) and observe it asynchronously over an MQTT event channel. Supported roles include orchestrator, worker, and reviewer."
-version: 2.0.0
+version: 2.1.0
 author: godopu
 license: MIT
 platforms: [linux, macos, windows]