[kvlonge]

Why

Model-mode sqb diff required a FROM:TO range and exactly one of --full, --schema-only or --bounded, and --key / --exclude-column had to be repeated for each value.

Changes

• sqb diff prod -s x compares prod with the active target, as sqb clone --from does; FROM:TO keeps working.
• With no mode flag, diff runs a full comparison after a size guard: row counts come from warehouse metadata on both sides, and any model over its side's limit, or of unknown size (views, missing metadata), stops the run before data is read, with the sizes and the commands to run instead. Explicit --full, --bounded and --schema-only bypass the guard.
• New [targets.<name>.diff] max_full_rows (positive integer or "unlimited", default 10,000,000), overridable in sqlbuild_local.toml.
• Row-count lookup on every built-in adapter; custom adapters report unknown by default.
• --key and --exclude-column take several values.
• Docs for cli/diff, concepts/diff and project configuration.

Verification

• Unit tests for config parsing, limits, error rendering, FROM/TO parsing and offline adapter lookups; DuckDB integration tests for the guard (under, over either side, unknown, unlimited, metadata-only queries before stopping); 12 new E2E cases.
• Focused pytest, ruff, fensu check and make check-ci.