Add gRPC protocol definition for HedgehogPanel in proto package

[Batacek]

gRPC integration — shared protocol, Daemon server, Panel client

Overview

Implements the full gRPC integration layer between HedgehogPanel (C#) and HedgehogDaemon (Rust). Defines a shared .proto contract and implements both sides — Daemon as gRPC server, Panel as gRPC client — verified by an end-to-end integration test.

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Checklist

• proto/hedgehog.proto — shared contract definition
• Daemon (Rust) — add tonic + prost, implement gRPC server
• Panel (C#) — add Grpc.AspNetCore + Grpc.Tools, implement gRPC client
• Integration test — mock server + client, verify end-to-end connectivity

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Protocol structure (hedgehog.v1)

Shared types

• ErrorCode — unified error enum used across all responses
• Status — daemon health status (STATUS_OK, STATUS_ERRORED, STATUS_UNKNOWN)
• AuthContext — reusable authentication context (panel_uuid + token) passed in every authenticated request

Endpoints defined

RPC	Auth	Description
PublicHealthCheck	❌	Basic liveness check, intentionally returns minimal information without authentication
DetailedHealth	✅	Full metrics (CPU, RAM, processes, uptime) including public health status
RegisterPanel	❌	Exchange a one-time installation code for a long-term token
Handshake	✅	Verify token validity for an existing Panel↔Daemon relationship

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Design decisions

• Public health intentionally omits daemon_uuid and version — endpoint is unauthenticated and publicly accessible, exposing daemon identity would be an unnecessary information leak
• DetailedHealthResponse embeds PublicHealthCheckResponse — reuses status, error_code and uptime fields without duplication
• ErrorCode is defined at package level — shared across all messages instead of being duplicated per-message
• Many-to-many Panel↔Daemon support via AuthContext — each Panel+Daemon pair has its own token, Daemon identifies the caller via panel_uuid + token lookup

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Compatibility guarantees

• Field tags are final and will never be reordered or reused
• Removed fields will always be marked with reserved
• New fields will always use new tag numbers
• Breaking changes will bump the package version to hedgehog.v2

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Files changed

• proto/hedgehog.proto
• Cargo.toml
• build.rs
• HedgehogPanel/HedgehogPanel.csproj
• HedgehogPanel/Infrastructure/Daemon/ (gRPC client)