Fix Peers API 500 + Add Delete Device to Devices List

TL;DR

Quick Summary: Fix HWID unique constraint violation causing 500 on POST /api/v1/peers by making HWID nullable; add delete button to Devices.vue list view

Deliverables:

Backend: HWID model change string → *string, fix CreatePeer/CreateDevice

Frontend: Delete button in Devices.vue table rows

Migration: SQL to convert existing empty HWIDs to NULL + container restart

Estimated Effort: Short Parallel Execution: YES

Context

Root Cause

Device.HWID is string with uniqueIndex. CreatePeer sets HWID: "" which collides with other devices having empty HWID → SQLSTATE 23505
Fix: make HWID *string (nullable), PostgreSQL treats NULLs as distinct in unique constraints

Delete Missing

Backend: DELETE /devices/:id exists at main.go:176, devicesHandler.Delete in devices.go:235
API: deleteDevice(id) exists in devices.ts:50
DeviceDetail: has delete button with confirm dialog
Devices.vue: Actions column only has View, Config, Firewall — no Delete

TODOs

1. Backend: Change HWID to *string in Device model

What to do:
- Edit apps/server-core/internal/models/models.go line 60:
  - Change HWID string \gorm:"column:hwid;uniqueIndex;size:64"``
  - To HWID *string \gorm:"column:hwid;uniqueIndex;size:64"``
Must NOT do:
- Don't change any other fields in the model
Recommended Agent Profile: unspecified-high (precise Go struct edit)

QA Scenarios:
```
Scenario: Verify build after model change
  Tool: Bash
  Steps:
    1. cd apps/server-core && go build ./...
  Expected Result: No compilation errors
  Evidence: .sisyphus/evidence/task-1-build.txt
```
2. Backend: Fix CreatePeer to not set empty HWID

What to do:
- Edit apps/server-core/api/peers.go — remove HWID: "" line (line 96)
- Since HWID is now *string, the zero value (nil) is correct — it won't violate unique constraint
- Keep RegTokenHash: "" as-is (no unique index on that)
QA Scenarios:
```
Scenario: Build passes after fix
  Tool: Bash
  Steps:
    1. cd apps/server-core && go build ./...
  Expected Result: Clean build
  Evidence: .sisyphus/evidence/task-2-build.txt
```
3. Backend: Fix CreateDevice to not set empty HWID

What to do:
- Edit apps/server-core/api/devices.go — verify Create function (line 84-89) doesn't set HWID
- It currently doesn't set HWID at all, so with *string it will default to nil — correct
- Verify Delete function (line 235-255) already works — it does, no changes needed

4. Migration: Convert existing empty HWIDs to NULL on server

What to do:

SSH into 172.20.8.191 and run SQL against the postgres container:

docker exec nexus-guard-suite-postgres-1 psql -U nexusguard -d nexusguard -c "UPDATE devices SET hwid = NULL WHERE hwid = '';"

Then restart server-core container:

docker restart nexus-guard-suite-server-core-1

QA Scenarios:

Scenario: Verify empty HWIDs are now NULL
  Tool: Bash
  Steps:
    1. docker exec nexus-guard-suite-postgres-1 psql -U nexusguard -d nexusguard -c "SELECT count(*) FROM devices WHERE hwid = '';"
  Expected Result: count = 0
  Evidence: .sisyphus/evidence/task-4-sql.txt

Scenario: Verify POST /api/v1/peers succeeds
  Tool: Bash
  Steps:
    1. Obtain auth token via POST /api/v1/auth/login with admin credentials
    2. POST /api/v1/peers with valid body (name, wg_server_id)
  Expected Result: 201 Created (not 500)
  Evidence: .sisyphus/evidence/task-4-peers-api.txt

5. Frontend: Add delete button to Devices.vue list

What to do:

Edit apps/dashboard-ui/src/views/Devices.vue

Add delete button in the Actions column (line 34-39), after Firewall button:

<button @click="handleDelete(device.ID, device.Name)" class="text-red-400 hover:text-red-300 font-bold">Delete</button>

Import deleteDevice from ../api/devices

Add handleDelete function:

const handleDelete = async (id: string, name: string) => {
  if (!confirm(`Delete device "${name}"? This will destroy its tunnel and all firewall rules.`)) return
  try {
    await deleteDevice(id)
    store.loadDevices()
  } catch (err: any) {
    alert(err.response?.data?.error || 'Failed to delete device')
  }
}

Must NOT do:

Don't remove the existing Config/Firewall buttons

Recommended Agent Profile: visual-engineering (Vue UI)