chore: adopt mg-tools — gitignore baseline for internal dev tooling

Adds the per-developer gitignore entries needed for MakeGov team members
who use mg-tools (an internal Claude Code plugin that provides shared
agents, skills, rules, and hooks across our repos).

Internal-focused only — no effect on the published SDK, its API, or
external contributors. Ignored paths:

- .claude-plugin/                     plugin pointer
- .claude/settings.json               merged Claude Code permissions
- .claude/settings.local.json         personal overrides
- .claude/mg-tools-integration.md     team-only plugin notes
- .mcp.json / .mcp.disabled.json      MCP server configs (per-dev)
- .mg-tools/                          scratch, config, diary, version
- .claude.bak.* / .cursor.bak.* / .mcp.json.bak.*   install backups
- CLAUDE.md                           per-developer AI-assistant context
                                      (each team member regenerates from
                                      mg-tools' sdk-python template)

Also fixes a missing trailing newline on the pre-existing 'examples/'
entry that would otherwise concatenate with any appended block.

External contributors don't need any of this. README, CONTRIBUTING,
and docs/ remain the contribution entry points.

Author: infinityplusone

.gitignore

@@ -149,4 +149,17 @@ Thumbs.db
 yoni/
 .cursor/*
 
-examples/
+examples/
+
+# --- mg-tools (per-developer; re-run 'mg-tools install' after clone) ---
+.claude-plugin/
+.claude/settings.json
+.claude/settings.local.json
+.claude/mg-tools-integration.md
+.mcp.json
+.mcp.disabled.json
+.mg-tools/
+.claude.bak.*
+.cursor.bak.*
+.mcp.json.bak.*
+CLAUDE.md