v0.5.49 release

v0.5.49 release notes for the GitHub Release v0.5.49 (release task: Issue #1406).

Tag state (verified against origin)

Ref	Object	Points at
`v0.5.49`	annotated tag `c867d4e9de54ddd1ac46279f8a349f86b403a652`	commit `89f4659d87ba37dcc5f932516062f8cb7b4237d8`

Claude plugin: add a root Agent Plugins 1.0 plugin.json so the same folder lists in awesome-copilot and the Cursor Marketplace (Issue #1404; PR #1408)