Add models.dev metadata-enrichment pipeline (providers P0c-2)

Provider /models listings that return bare ids (OpenAI-style) get context
windows, thinking levels, image support, and display names from models.dev:
kigi-models owns the transform (parse_api_json — ONE field interpretation
for the bundled snapshot AND runtime refreshes), enrich_wire_model fills
gaps with wire values always winning and model availability strictly
wire-truth. Spec rows gained models_dev_id + wire_serves_metadata; all
three current platforms are wire-served, so this pipeline is provably
inert for them (byte-identical catalogs, zero egress, zero ~/.kigi writes
— adversarially verified).

Shell side: enrichment_fetch with a 24h disk cache guarded by binary
version + keep-set + future-stamp sanity (a registry change or downgrade
refetches instead of serving a catalog missing new providers), refresh of
https://models.dev/api.json filtered to registry ids, KIGI_MODELS_DEV_URL
override with case/whitespace-tolerant kill switch, fallback chain
fresh-cache > refresh > stale-cache > bundled (each step logged). The
fast path returns an empty catalog without forcing the bundled parse.

From the review: blast-radius-confined parsing (one drifted provider on
models.dev warn-skips instead of failing the whole refresh), registry-
coverage and field-coverage tests guarding script/parser drift, a path-
injectable core with 8 state-machine tests (one of which caught a guard
patch that had failed to apply), _meta provenance stamp in the snapshot,
and models.dev (MIT) attribution in NOTICE. Snapshot: 29 providers, 1124
models, 246KB, regenerated by scripts/gen_enrichment_snapshot.py (pure
filter, no transform).

crates/codegen/kigi-shell/src/agent/mod.rs

@@ -4,6 +4,7 @@ pub mod auth_method;
 pub mod chat_modes;
 pub mod config;
 pub mod config_model_override_parse;
+pub(crate) mod enrichment_fetch;
 mod ext_parsers;
 pub(crate) mod feedback_client;
 pub mod folder_trust;