Layered configuration

As an advanced user, I want to override any config key at the global or project level, so that booping fits my machine and my codebase without touching the plugin.

Scenarios§

1. The user sets a key in ~/.config/booping/config.yaml, and it applies to every project on the machine.
2. The user sets the same key in the Project Vault's config.yaml, and the project's value wins for that project.
3. The user reads the merged value back with the CLI to see what a run will use.
4. The user declares a query spec or a template tree at a config path, then runs it with booping query --config or writes it with booping create, each write printed as a unified diff.

Edge cases§

• A list is overridden at a later level: it replaces the earlier list wholesale, it is not merged.
• booping create meets an existing target: it skips it unless --force.
• A write leaves a file unchanged: nothing is printed.
• A render needs to be reproducible: the macros are stubbed instead of run.

Criteria§

• Any key can be overridden in ~/.config/booping/config.yaml or the Project Vault's config.yaml, later levels winning.
• Query specs declared at any config path run with booping query --config or the | query filter; template trees are written with booping create, skipping an existing target unless --force.
• booping create and booping frontmatter-update print every write as a unified diff, silent when a file is unchanged.
• Argv macros under core.macros carry a command: and a cwd: repo|vault, and can be stubbed for reproducible renders.
• booping config-get reads any merged value and booping marker-set sets marker keys; core.plans.glob and core.research_agent are ordinary overridable keys.