feat(sync): show device hostnames in Linked devices table; document sync fully

- Sync: use OS hostname for each device in Linked devices table; persist
  deviceNames in state and merge on save/apply so peers see each other's names
- Docs: expand SYNC.md (linked devices table, replace-state modal, multi-device,
  offline); NATIVE-HOST getSyncStatus (deviceId, syncGroupId, linkedDevices,
  deviceName/name); ARCHITECTURE sync-manager and autopass paths; README
  features/dashboard/file locations/doc link; BACKUP and SECURITY cross-refs

docs/ARCHITECTURE.md

@@ -350,10 +350,13 @@ All state is owned by the native host and persisted to `state.json` next to the
   ],
   "rdpConnections": [
     { "id": "rdp-abc123", "label": "Work PC", "hsUrl": "hs://xyz...", "type": "vnc", "port": 5901, "width": 1280, "height": 720, "username": "", "passwordB64": "cGFzc3dvcmQ=" }
-  ]
+  ],
+  "deviceNames": { "a1b2c3d4e5f6": "macbook-pro", "b2c3d4e5f678": "work-laptop" }
 }
 ```
 
+When sync is used, `deviceNames` (optional) maps each device’s short hex ID to its OS hostname so the Linked devices table can show names instead of “Device 2”, etc.
+
 Additional settings (e.g. `notifyOnTunnelError`, `backupIntervalHours`, `tunnelAutoReconnect`, `latencyPingEnabled`, `latencyPingIntervalMs`) may be present; see `native-host/holesail-manager/state.js` `SETTINGS_DEFAULTS`.
 
 ## Native host lifecycle

docs/NATIVE-HOST.md

@@ -525,15 +525,16 @@ Return whether this device is linked for sync, optional invite/last-synced info,
   "invite": "optional invite string if one was created",
   "lastSyncedAt": 1710000000000,
   "deviceId": "a1b2c3d4e5f6",
+  "deviceName": "macbook-pro",
   "syncGroupId": "f6e5d4c3b2a1",
   "linkedDevices": [
-    { "id": "a1b2c3d4e5f6", "isCurrent": true },
-    { "id": "b2c3d4e5f678", "isCurrent": false }
+    { "id": "a1b2c3d4e5f6", "isCurrent": true, "name": "macbook-pro" },
+    { "id": "b2c3d4e5f678", "isCurrent": false, "name": "work-laptop" }
   ]
 }
 ```
 
-When linked, `deviceId` is a short hex ID for this device’s writer key and `syncGroupId` is a short hex ID for the shared discovery key. `linkedDevices` is populated from the autopass active writers; it may contain only this device until other peers have replicated at least once.
+When linked, `deviceId` is a short hex ID for this device’s writer key, `deviceName` is the OS hostname of this device, and `syncGroupId` is a short hex ID for the shared discovery key. `linkedDevices` is populated from the autopass active writers; each entry includes `name` (hostname) when known from synced state, so other peers’ hostnames appear after they have replicated at least once. It may contain only this device until other peers have replicated.
 
 ---
 

docs/SYNC.md

@@ -19,8 +19,8 @@ Holesail Browser can sync its state across two devices using [autopass](https://
 
 When linked, the Sync page shows a **Linked devices** table:
 
-- **This device** — This machine’s device ID (a short hex fingerprint of its autopass writer key).
-- **Device 2**, **Device 3**, … — Other devices in the same sync group, each with their own ID. Other peers appear in the table after they have replicated at least once; if the other device is offline or has not yet synced, you may only see “This device” until replication runs.
+- **Device name** — Each device is shown by its **hostname** (the OS hostname of the machine, e.g. `macbook-pro`, `work-laptop`). Hostnames are synced in state so once a device has replicated at least once, other peers will see its hostname in the table. If a hostname is not yet known, the table falls back to “This device” for the current machine or “Device 2”, “Device 3”, etc. for others.
+- **Device ID** — The short hex ID (fingerprint of the device’s autopass writer key) is shown next to each name. Other peers appear in the table after they have replicated at least once; if the other device is offline or has not yet synced, you may only see this device until replication runs.
 - **Sync group** — A shared ID (fingerprint of the discovery key) that is the same on every device in the group. You can confirm both devices are in the same group by checking that the Sync group ID matches on each.
 
 ## More than two devices