describe refuses a scan carrying a scope or field the format tables do not know: every new omx-clap-core scan field breaks every add with -531 #155

Found reviewing PR #154. read_dump in src/describe.c refuses the --fields dump on an unknown scope ("dump line 78: panel is no clap scope" on main with omx-clap-core 0.20.0) and on a field with no table row (" : the field has no row"). PR #154 adds the six panel scopes and 29 rows, so 0.20.0 describes again; the next omx-clap-core release that adds a scan field breaks every add again, and the user sees -531 per plugin with no hint that the daemon is simply older than the scanner.

The strictness itself is the house rule (the format tables declare exactly what exists; docs/formats.md), so this is not a request to drop fields silently. Wanted instead:

1. One refusal at the right altitude: when the dump carries a scope or field the tables do not know, describe answers one code that says "scanner newer than the daemon's tables: from omx-clap-scan " and names the daemon version that would know it, instead of -531 per plugin.
2. A floor-and-ceiling check at daemon start against omx-clap-scan --version (the floor already exists for the panel test), logged once.
3. The release discipline written down in docs/formats.md: an omx-clap-core release that adds a scan field ships with the plugin-hostd row in the same wave (the consumer-floors wave), and the worker image pins both.