feat: add full CRUD for all Netbird API resources

[ZILosoft]

Summary

This PR extends the MCP server from read-only list operations to full CRUD coverage across all major Netbird API resources.

New HTTP methods on NetbirdClient

• Post(ctx, path, body, v) — for create operations
• Delete(ctx, path) — for delete operations
• Patch(ctx, path, body, v) — for partial updates
• Fixed status check to accept both 200 OK and 204 No Content (DELETE responses)

Extended existing tools (get / create / update / delete added)

Resource	New tools
Peers	get_netbird_peer, update_netbird_peer, delete_netbird_peer, get_netbird_peer_accessible_peers
Groups	get_netbird_group, create_netbird_group, update_netbird_group, delete_netbird_group
Policies	get_netbird_policy, create_netbird_policy, update_netbird_policy, delete_netbird_policy
Networks	get_netbird_network, create_netbird_network, update_netbird_network, delete_netbird_network
DNS Nameservers	get_netbird_nameserver, create_netbird_nameserver, update_netbird_nameserver, delete_netbird_nameserver
Posture Checks	get_netbird_posture_check, create_netbird_posture_check, update_netbird_posture_check, delete_netbird_posture_check

New tool files

File	Tools
tools/network_resources.go	Full CRUD for network resources (/networks/{id}/resources)
tools/network_routers.go	Full CRUD for network routers (/networks/{id}/routers)
tools/dns_settings.go	get_netbird_dns_settings, update_netbird_dns_settings
tools/setup_keys.go	Full CRUD for setup keys
tools/users.go	Full CRUD + get_netbird_current_user, invite_netbird_user
tools/accounts.go	list_netbird_accounts, update_netbird_account
tools/routes.go	Full CRUD for routes
tools/events.go	list_netbird_events with page/limit pagination
tools/tokens.go	List, get, create, delete for personal access tokens

Test plan

• go build ./... compiles without errors
• go test ./... passes all existing tests
• Verify list tools still work as before (no regression)
• Test create/delete cycle on a non-production Netbird instance