docs: mark 8 ROADMAP items DONE (78,84,103,107,108,110,116,119)

78: plugins CLI wired as CliAction::Plugins (verified runtime)
84: dump-manifests fixed 2026-06-03
103: agents discovery handles .md with YAML frontmatter (#442)
107: hook validation in doctor JSON (verified runtime)
108: CLI typos → command_not_found (verified runtime)
110: ConfigLoader discovers project/user/local configs
116: unknown keys now emit warnings not errors (#441)
119: bare_slash_command_guidance checks aliases (#772)

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Author: 2 people