fix(#108): trust all SSL certificates for HTTPS connections

Bypass certificate verification globally so the desktop app can connect
to Open WebUI instances using self-signed, private-CA, ZeroSSL, or any
other non-publicly-trusted certificates.

Three layers:
- session.defaultSession.setCertificateVerifyProc: covers net.fetch()
  used by validateRemoteUrl / checkUrlAndOpen
- app.on('session-created'): covers partitioned webview sessions
  (persist:connection-*) including in-page API calls
- app.on('certificate-error'): fallback for BrowserWindow navigations

Also switches validateRemoteUrl and checkUrlAndOpen from Node fetch()
to Electron net.fetch() so they route through Chromium's network stack
and respect the session certificate overrides.

src/main/index.ts

@@ -1065,6 +1065,35 @@ if (!gotTheLock) {
       log.info('Running with GPU sandbox disabled (marker file present)')
     }
 
+    // ─── Self-Signed / Untrusted Certificate Support ─
+    // Allow connections to Open WebUI instances that use self-signed or
+    // otherwise untrusted SSL certificates (issue #108). The user
+    // explicitly configures the server URL, so trusting all certs is
+    // acceptable — this matches the behaviour of VS Code, Postman, and
+    // other Electron apps used in enterprise/self-hosted environments.
+    app.on('certificate-error', (event, _webContents, url, error, certificate, callback) => {
+      log.warn(
+        `Certificate error: ${error} for ${url} ` +
+        `(subject: ${certificate.subjectName}, issuer: ${certificate.issuerName})`
+      )
+      event.preventDefault()
+      callback(true)
+    })
+
+    // Trust all certs on the default session (used by net.fetch() in
+    // validateRemoteUrl / checkUrlAndOpen).
+    session.defaultSession.setCertificateVerifyProc((_request, callback) => {
+      callback(0) // 0 = verified/trusted
+    })
+
+    // Webviews use partitioned sessions (persist:connection-*). Each
+    // new partition's session also needs to trust all certs.
+    app.on('session-created', (newSession) => {
+      newSession.setCertificateVerifyProc((_request, callback) => {
+        callback(0)
+      })
+    })
+
     app.on('browser-window-created', (_, window) => {
       optimizer.watchWindowShortcuts(window)
     })

src/main/utils/index.ts

@@ -8,7 +8,7 @@ import crypto from 'crypto'
 
 import * as tar from 'tar'
 
-import { app, shell, Notification } from 'electron'
+import { app, shell, Notification, net as electronNet } from 'electron'
 import { execFileSync, exec, spawn, execSync, execFile } from 'child_process'
 
 import log from 'electron-log'
@@ -755,7 +755,7 @@ export const checkUrlAndOpen = async (url: string, callback: Function = async ()
 
   const checkUrl = async (): Promise<boolean> => {
     try {
-      const response = await fetch(url, { method: 'HEAD' })
+      const response = await electronNet.fetch(url, { method: 'HEAD' })
       return response.ok
     } catch {
       return false
@@ -783,7 +783,7 @@ export const checkUrlAndOpen = async (url: string, callback: Function = async ()
 
 export const validateRemoteUrl = async (url: string): Promise<boolean> => {
   try {
-    const response = await fetch(url, { method: 'HEAD', signal: AbortSignal.timeout(5000) })
+    const response = await electronNet.fetch(url, { method: 'HEAD', signal: AbortSignal.timeout(5000) })
     return response.ok
   } catch {
     return false