[Feature] Relay model ids with a month-day date suffix (deepseek-ai/deepseek-v4-pro-0813) miss the built-in catalog

[L4XB]

Split out of #786 (part 2 of that report) so it can be closed by a focused change; part 1 (a configurable auto-compaction threshold) stays tracked in #786.

Problem

Relays expose official models as <vendor>/<id>-MMDD, for example deepseek-ai/deepseek-v4-pro-0813. normalizeModelIdCandidates in crates/agent-ui/src/lib/models/modelCatalog.ts strips the vendor prefix and a full -YYYYMMDD date, but not the four-digit month-day form, so the id misses deepseek-v4-pro (contextWindow 1,000,000 / maxOutputToken 384,000) and getProviderModelDefaults falls back to the provider defaults (400,000 / 142,000). The context window is undercounted by about half and auto-compaction fires far too early.

Proposed behavior

Also strip a trailing -MMDD (valid month and day only, and only when no full date is present) for the raw id and its last path segment, so deepseek-ai/deepseek-v4-pro-0813 resolves to deepseek-v4-pro. Ids that exist in the catalog with their date (deepseek-r1-0528) keep matching themselves first.

Scope

crates/agent-ui/src/lib/models/modelCatalog.ts (candidate chain) and crates/agent-gui/test/models/model-catalog.test.mjs. No UI change.