feat: strip request params models declare unsupported

[aaliboyev]

Some models reject sampling params the adapters forward unconditionally (#394, #395) — customer requests fail with upstream 400s the relay could prevent. This makes param support capability data, gated once in code:

• model.Capabilities gains unsupportedParams (inverted: zero value = everything supported; unknown names inert). Mirrored in the SDK catalog structs; cmd/modelsdev-import now maps models.dev's explicit temperature: false into it (*bool so an absent field is never misread).
• Dispatch strips flagged params pre-upstream: canonical path via the sampling opts, byte-pass path via Spec.ParamPaths (wire locations declared on the Spec literals; same json.RawMessage technique as the model-field rewrite — bodies with nothing to strip pass through byte-identical). The batch runner reuses the strip via inference.StripUnsupportedParams; WS already flows through Dispatch. Proxy mode is deliberately untouched.
• Never silent: every drop sets X-WR-Warnings: dropped_params=… and increments relay_dropped_params_total{param,model}.

Fixing a newly drifted model then needs only a catalog data change — no adapter or relay release.

Fixes #394. Fixes #395 (data side: wyolet/relay-catalog#27).