manifest v5.51.0

✨ Minor Changes

• 910b191: Add custom header-triggered routing tiers. Configure a tier keyed to an HTTP header key+value pair (e.g. x-manifest-tier: premium) and every matching request routes directly to that tier's model, overriding specificity and complexity. Each tier gets a user-picked name + color that shows as a badge on the message row. The create modal autocompletes the header key from the keys Manifest has already seen in the last 7 days, grouped by the SDK that sent them, with example values. Sensitive headers (authorization, cookie, …) are blocked from being used as match rules.