web: capture the real GraphQL error message at the network layer

[sdunster]

Neither the Relay field-logger nor the message-recovery fix (prior
commit) can surface the real message for most server-side field
failures: async-graphql omits a failed field's key from the response
entirely rather than sending it as explicit null, and Relay's
normalizer only attaches an error to a record when it sees an
explicit null — an absent key takes an earlier branch that warns and
returns before ever consulting the error list. So
relay_field_payload.error (the one Relay event that carries a
message) essentially never fires for a real query-side resolver
failure, and the field logger's own console output shows a path with
no explanation.

fetchGraphQL now reads response.errors directly off every parsed
response, for every operation kind, before Relay ever touches it —
sidestepping the normalizer question entirely. Each response with
errors gets an immediate [graphql-error] console log with the full
raw error list (message, path, locations, extensions), and the
messages are buffered via relayFieldLogger's
recordServerErrorMessages, so describeCaughtError can still recover
them later for on-screen display once a generic Relay throw reaches
an error boundary. This fixes the console-logging gap immediately,
independent of whether @throwOnFieldError is applied to the query
that failed.

Query captures never throw, unlike the existing mutation path
(unaffected, still throws MutationFieldError) — some field.error
combinations are legitimate degradation (e.g. an absorber field
resolving to null), and query components already have their own
suspense/render flow to interrupt only when a boundary is meant to
catch something.

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• -> web: capture the real GraphQL error message at the network layer #155
• web: show the real message for Relay's generic field-error throws #154
• web: log Relay field errors #132