feat(asset): report HOST category and send asset-scoped network fields on registration (#207)

[SamuelHassine]

Summary

Adapts the agent registration payload to the OpenAEV asset taxonomy remodel:

• Network fields renamed to the asset level: endpoint_ips -> asset_ips, endpoint_hostname -> asset_hostname, endpoint_mac_addresses -> asset_mac_addresses.
• Platform / arch / agent_version stay endpoint-scoped; asset_name / asset_external_reference / asset_category (HOST) are asset_*.
• The hostname is now computed once and reused for asset_name and asset_hostname (review feedback: avoids a redundant syscall and any inconsistency between the two fields), and the payload keys are grouped by scope (asset_, endpoint_, agent_*) for readability. Wire format unchanged.

The backend keeps a JsonAlias on the legacy endpoint_* names so already-deployed agents keep registering until they self-update; this aligns the agent source with the new canonical wire names used by the platform, injectors, collectors and the Python client.

The implant needs no change (it sends no endpoint_* asset fields).

Closes #207

Test plan

• CI green on all platforms (fmt, audit, clippy on ubuntu/windows/macos, tests and builds on all six targets, coverage, installer script packaging).
• Build the agent and register against an OpenAEV backend that includes the asset taxonomy remodel; confirm the endpoint is created with hostname / IPs / MAC addresses populated.

[Copilot]

Pull request overview

Updates the agent registration payload (src/api/register_agent.rs) to align with the OpenAEV asset taxonomy remodel by emitting canonical asset_* network fields and reporting the asset category as HOST.

Changes:

• Renamed network registration fields from endpoint_* to asset_* (asset_ips, asset_hostname, asset_mac_addresses).
• Added asset_category: "HOST" to the registration payload.
• Kept endpoint-scoped fields unchanged (endpoint_platform, endpoint_arch, endpoint_agent_version).

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[SamuelHassine]

Review-and-fix pass complete:

• Addressed the Copilot review comment: hostname::get() is now called once and reused for asset_name and asset_hostname (commit 5737151). The payload keys were also grouped by scope (asset_, endpoint_, agent_*); the wire format is unchanged.
• Independent review of src/api/register_agent.rs and its caller (keep_alive.rs ping loop) found no further issues: registration errors are logged and retried on the next 2-minute ping, list_jobs in manage_jobs.rs sends no renamed field, and the backend keeps JsonAlias compatibility for legacy endpoint_* names.
• All review threads are resolved and all CI checks are green on the latest commit (fmt + audit, clippy and tests/builds on ubuntu/windows/macos x86_64 + arm64, coverage, installer packaging, signed commits, PR title validation, CLA).
• PR description updated to reflect the final state.

Remaining (non-CI) blocker: the branch protection requires one approving review, and the PR author cannot self-approve - a maintainer approval is the only step left before merge.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.