feat(signals): accept the decisions model mode alongside evaluation

[devin-ai-integration]

Summary

LiteLLM is adding cost map rows for decision models with mode: decisions. The existing rows keep the legacy mode: evaluation (BerriAI/litellm#45474 makes the gateway accept both). Lens only matched evaluation, so a decisions model was never discovered for Signals, and saving a Signals config with one was rejected

This PR treats both values the same through one predicate, lens_contract::activity::is_decisions_mode, used in gateway discovery (gateway/discovery.rs) and the Signals save check (server/src/signals.rs). The UI filter systemOneModels uses a matching isDecisionsMode, and docs/signals.md names both modes

Tests

discovery.rs has a new test that discovers a decisions model and an evaluation model into the evaluation deployments. gateway_http.rs now refreshes a gateway reporting one of each, saves a Signals config on the decisions model and still rejects a chat model. There are also unit tests for both predicates

Caveats

The bundled model_catalog.json parses with litellm-model-catalog pinned at 3969348, which has no Mode::Decisions. One decisions row makes Catalog::parse fail for the whole file, so refreshing that snapshot after LiteLLM adds decisions rows needs the pin bumped past BerriAI/litellm#45474 first. The same bump should let decisions/src/transport.rs accept Mode::Decisions next to Mode::Evaluation

Link to Devin session: https://app.devin.ai/sessions/290da858f1bd412dbb3b36b7d880974c
Open in Devin Desktop: https://app.devin.ai/desktop/session/290da858f1bd412dbb3b36b7d880974c?variant=devin
Requested by: @kerry-berri

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Note

Devin errored when opening this Pull Request as kerry-berri.
As a fallback, Devin opened this PR as itself.

[devin-ai-integration]

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