Document -short flag, update linting baseline, clarify bd edit MCP exclusion

- Enhanced CONTRIBUTING.md with -short flag usage guidance
- Updated LINTING.md: 22 issues baseline (down from 34)
- Added MCP exclusion note for bd edit command in AGENTS.md

Closes bd-iov0, bd-aec5439f, bd-fd8753d9

AGENTS.md

@@ -172,6 +172,8 @@ bd update <id> [<id>...] --status in_progress --json
 bd update <id> [<id>...] --priority 1 --json
 
 # Edit issue fields in $EDITOR (HUMANS ONLY - not for agents)
+# NOTE: This command is intentionally NOT exposed via the MCP server
+# Agents should use 'bd update' with field-specific parameters instead
 bd edit <id>                    # Edit description
 bd edit <id> --title            # Edit title
 bd edit <id> --design           # Edit design notes