Single vocab table loading

[nicoloesch]

Summary

• Fixes Allow to load a singular vocabulary table #30

• load_vocab_source() gains an optional tables: list[str] | None = None parameter

  • When provided, only models whose __tablename__ is in the list are loaded
  • the all-required-files preflight check is skipped
  • an absent CSV for a named table is an error rather than a silent skip.

• Unknown table names are validated eagerly against the full vocabulary table set before any DB work begins.

• load-vocab-source CLI command gains a repeatable --table <name> option that maps directly to the new parameter. No --table flags = existing all-tables behaviour, unchanged.

Test plan

• load-vocab-source --table concept loads only concept
• load-vocab-source --table concept --table vocabulary loads exactly those two
• load-vocab-source --table not_a_table raises ValueError before any DB connection
• load-vocab-source (no flag) behaves identically to the previous version
• Missing CSV for an explicitly named table produces a clear RuntimeError
• --table with a sparse source dir skips the all-required-files preflight correctly
• CLI fake_load_vocab_source stub updated to accept tables kwarg (regression guard)