Plugins are now verified against ~/.config/gnoma/plugins.pins.toml at
load time. Each plugin's plugin.json bytes are hashed (SHA-256) and:
- recorded automatically on first load (TOFU) with a prominent warning
- compared on subsequent loads
- refused with a clear error if the hash drifted, without overwriting
the pin so the user can review and re-enrol deliberately
Pin-store I/O failures degrade to load-without-pinning rather than
locking the user out of previously-trusted plugins.
Closes audit finding C2. See ADR-003 for the decision rationale and
docs/plugins-trust.md for the end-user trust model.
