refactor(gui): collapse public server and standalone into initial peer list (#2017)

The GUI exposed three networking modes: public server, manual, and standalone. In practice EasyTier does not have a server/client role distinction here. Those options only mapped to different peer bootstrap shapes, which made the product model misleading and pushed users toward a non-existent "public server" concept.

This change rewrites the shared configuration UX around initial nodes. Users now add or remove one or more initial node URLs directly, and the UI explains that EasyTier networking works like plugging in a cable: once a node connects to one or more existing nodes, it can join the mesh. Initial nodes may be self-hosted or shared by others.

To preserve compatibility, the frontend keeps the legacy fields and adds normalization helpers in the shared NetworkConfig layer. Old configs are read as initial_node_urls, while saves, runs, validation, config generation, and persisted GUI config sync still denormalize back into the current backend shape: zero initial nodes -> Standalone, one -> PublicServer, many -> Manual. This avoids any proto or backend API change while making old saved configs and imported TOML files load cleanly in the new UI.

Code changes:

- add initial_node_urls plus normalize/denormalize helpers in the shared frontend NetworkConfig model

- remove the mode switch and public-server/manual specific inputs from the shared Config component and replace them with a single initial-node list plus explanatory copy

- update Chinese and English locale strings for the new terminology

- normalize configs received from GUI/web backends and denormalize them before outbound API calls

- normalize GUI save-config events before storing them in localStorage so legacy payloads remain editable under the new model

easytier-web/frontend-lib/src/locales/en.yaml

@@ -3,6 +3,14 @@ networking_method: Networking Method
 public_server: Public Server
 manual: Manual
 standalone: Standalone
+initial_nodes: Initial Nodes
+initial_nodes_help: |
+  EasyTier does not distinguish between server and client roles.
+  • Filling in Initial Nodes = plugging in the cable and joining an existing network.
+  • Leaving it empty = the node starts alone until others connect to it, or you connect it later yourself.
+  • Direct or indirect connectivity, including through relay nodes, can form one network.
+  Initial nodes can be your own nodes or ones shared by others.
+initial_node_placeholder: "Example: tcp://node.example.com:11010"
 virtual_ipv4: Virtual IPv4
 virtual_ipv4_dhcp: DHCP
 network_name: Network Name
@@ -26,6 +34,7 @@ error_msg: Error Message
 detail: Detail
 add_new_network: New Network
 add_peer_url: Add Peer
+add_initial_node: Add Initial Node
 add_listener_url: Add Listener
 add_mapped_listener: Add Mapped Listener
 del_cur_network: Delete Current Network