Agent Skills: wiring-application-config

Load, merge, and validate layered application configuration (defaults plus a user YAML/TOML/JSON file or a stored settings object) so a mis-wired or misspelled key fails loudly instead of silently reverting to the default — sections the code reads that exist nowhere, sections that exist but nothing reads, unvalidated recursive merges, `bool`-passes-as-`int`, defaults aliased by a shallow merge, falsy-but-valid values killed by `or`/`||`, partial write-backs that are stickier than a missing file, and bootstrap ordering that swallows the loader's own warnings. Use when adding a config key, writing or reviewing a config loader/merge/schema, reading a setting in a new module, persisting user settings, wiring logging from config, or debugging a setting that "has no effect".