Add button fields with simple row actions

## Goal

A button field plus a small library of safe row-level actions you can wire to it: set a property, clear a property, create a related row, duplicate the current row. Aimed at making common workflows one-click instead of multi-step.

## Scope

* New field type, button, that stores its action configuration as field meta.
* The v0 action library:
* Set a property to a value.
* Clear a property.
* Create a row in a related collection, with optional prefilled fields.
* Duplicate the current row.
* Configuration UI: pick the action and fill in its parameters.
* Server-side click logs as an audit trail (no fancy UI).

## Out of scope

* Scheduled or background automations (no execution model yet).
* Multi-step actions or chaining.
* External integrations (webhooks, Slack, and the rest).
* Automatic triggers (e.g., "when status changes to Done, do X").

## Acceptance criteria

* You can add a button field, pick an action, and configure its parameters.
* Clicking the button performs the action against the current row and refreshes the affected fields.
* Failed actions surface a clear error.
* Each click writes a server-side log entry.

No files, tests, or entry points are named. Begin by locating the field-definition and metadata path, the configuration UI, the row-action execution path, and server-side logging; done means all four listed actions can be configured, run against the current row, refresh affected fields, report failures clearly, and log each click.

Written by the indexing model from the issue text.