feat(core): add WireGuard core management support

[x0sina]

Summary
This PR adds full panel-side support for managing WireGuard cores while preserving the existing Xray flow. The implementation is additive: Xray logic remains intact, WireGuard is introduced through backend_type, and the existing group-to-inbound assignment model is reused instead of forking a separate WireGuard path.

What Changed

• Added backend_type support for core configs, including persistence and migration with existing records defaulting to xray.
• Added panel-side WireGuard core parsing/validation via a new WireGuard core config implementation.
• Generalized CoreManager and node startup so nodes start with the correct backend type and only send Xray-only fields when relevant.
• Extended user proxy settings with a wireguard section containing private_key, public_key, and peer_ips.
• Updated node serialization so synced users include wireguard_public_key and wireguard_peer_ips.
• Added backend validation enforcing the current node/bridge limitation of at most one WireGuard interface per user.
• Added automatic WireGuard keypair preparation and peer IP allocation for users assigned to exactly one WireGuard interface.
• Updated dashboard core/user forms to support WireGuard with minimal UI changes and no Xray regression.
• Generalized node/core version presentation with additive core_version handling while keeping xray_version compatible.

Behavior Guarantees

• Existing Xray create/update/delete/validate/sync/group flows remain unchanged.
• Existing Xray fallback and excluded inbound behavior remains backend-scoped and intact.
• Groups still assign users through inbound_tags; WireGuard now exposes interface_name through that same path.
• Mixed assignment is allowed for Xray + one WireGuard interface.
• Multiple WireGuard interfaces for one user are rejected clearly at the panel layer.

Remaining Limitations

• The panel still enforces one WireGuard interface per user because the current node/bridge contract supports only one WireGuard proxy object per user.
• Node DB/API compatibility still relies on the existing xray_version field; core_version was added logically at the panel/model layer, not as a full DB rename.
• WireGuard node core version updates use manual version entry in the dashboard; only Xray-backed nodes use the Xray release picker.

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