Adds [tools] section to config with boolean toggles for each MCP tool.
All tools enabled by default; conditionally registered based on config.

Wizard uses multi-select checkbox UI for tool selection during fresh
setup and reconfiguration. Example config and summary updated
accordingly.

Also fixes stale module paths in exhaustruct exclusions and disables
ireturn linter (interface returns are intentional in shared package).

Assisted-by: Claude Opus 4.5 via Crush

Upgrade github.com/mailru/easyjson from v0.7.7 to
v0.9.1. Go module system also updated transitive
dependencies and removed unused ones (golang.org/x/mod,
golang.org/x/net, golang.org/x/tools).

All tests and checks pass successfully.

Co-Authored-By: Crush <crush@charm.land>