v1.2.1 — documentation updates

Documentation and example updates.

• The reasoned-pairs probe under examples/ now takes its stores, its models and its endpoint from the environment — FORNIXDB_PROBE_STORES, FORNIXDB_PROBE_MODELS, FORNIXDB_PROBE_ENDPOINT — instead of values fixed in the file, so it runs anywhere without editing it. Unset, it probes this machine's default store with one small local model.

That probe asks whether a real, lived-in store holds enough reasoned structure to be worth mining, so being able to point it at your own stores is the whole point of running it.

No functional change to FornixDB itself. 987 tests.