docs(roadmap): add #407 — config files[].loaded:false no load_error; merged_keys ambiguous

[code-yeongyu]

Pinpoint #407

config --output-format json with 5 files, 3 not loaded:

{"files":[
  {"loaded":false,"path":"~/.claw.json","source":"user"},     // missing? parse error? skip?
  {"loaded":true,  "path":"~/.claw/settings.json","source":"user"},
  {"loaded":true,  "path":".claw.json","source":"project"},
  {"loaded":false,"path":".claw/settings.json","source":"project"},
  {"loaded":false,"path":".claw/settings.local.json","source":"local"}
],"loaded_files":2,"merged_keys":2}

No not_found/load_error/skip_reason on loaded:false entries. Also merged_keys:2 semantics unclear.

ROADMAP.md only