feat(investigations): Add Sentry-Seer orchestration protocol

[arslnb]

Adds the private bidirectional protocol between Sentry's investigation control plane and Seer. Sentry can issue signed create, read, and command requests with deterministic creation identity, validated responses, and organization-bound viewer context.

The Seer callback requires a signed viewer context matching the requested organization, validates a bounded versioned event envelope, and durably stages sequenced events with replay and collision handling. It deliberately reports events as pending until the reducer follow-up applies them, so this PR does not mutate projections or activate execution.

This is stacked on #123086. Before execution wiring lands, the Seer runtime PR must align its source models with Sentry's canonical metric context and regenerate its typed RPC bindings for deliver_investigation_event. Frontend-owned embed declarations remain in the evidence-rendering PR because backend and frontend changes cannot deploy atomically.

[cursor]

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[cursor]

Command payload sent in snake_case

Medium Severity

dispatch_investigation_orchestration_command spreads command.payload onto the Seer request without converting keys back to camelCase. Stored payloads come from command validators as snake_case, so fields such as timeRange, targetId, and hypothesisId go out as time_range, target_id, and hypothesis_id. The rest of this protocol, including create source.timeRange, uses camelCase on the wire, so those commands will not match Seer's contract.

 

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