feat(cups): add manual printer addition by IP/hostname (#1868)

Add a new "Add by Address" flow in the printer settings that allows
users to manually add printers by IP address or hostname, enabling
printing to devices not visible via mDNS/Avahi discovery (e.g.,
printers behind Tailscale subnet routers, VPNs, or across network
boundaries).

Go backend:
- New cups.testConnection IPC method that probes remote printers via
  IPP Get-Printer-Attributes with /ipp/print then / fallback
- Input validation with host sanitization and protocol allowlist
- Auth-aware probing (HTTP 401/403 reported as reachable)
- lpadmin CLI fallback for CreatePrinter/DeletePrinter when
  cups-pk-helper polkit authorization fails

QML frontend:
- "Add by Address" toggle alongside existing device discovery
- Manual entry form with host, port, protocol fields
- Test Connection button with loading state and result display
- Smart PPD auto-selection by probed makeModel with driverless fallback
- All strings use I18n.tr() with translator context

Includes 20+ unit tests covering validation, probe delegation, TLS
flag propagation, auth error detection, and handler routing.

quickshell/translations/template.json

@@ -769,6 +769,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Add by Address",
+    "translation": "",
+    "context": "Toggle button to manually add a printer by IP or hostname",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Adjust the number of columns in grid view mode.",
     "translation": "",
@@ -1994,6 +2001,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Caps Lock is on",
+    "translation": "",
+    "context": "",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Center Section",
     "translation": "",
@@ -2834,6 +2848,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Connection failed",
+    "translation": "",
+    "context": "Status message when test connection to printer fails",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Contains",
     "translation": "",
@@ -3842,6 +3863,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Discover Devices",
+    "translation": "",
+    "context": "Toggle button to scan for printers via mDNS/Avahi",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Disk",
     "translation": "",
@@ -5711,6 +5739,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Got It",
+    "translation": "",
+    "context": "",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Goth Corner Radius",
     "translation": "",
@@ -6145,6 +6180,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Host",
+    "translation": "",
+    "context": "Label for printer IP address or hostname input field",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Hostname",
     "translation": "",
@@ -6236,6 +6278,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "IP address or hostname",
+    "translation": "",
+    "context": "Placeholder text for manual printer address input",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "ISO Date",
     "translation": "",
@@ -9638,6 +9687,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Port",
+    "translation": "",
+    "context": "Label for printer port number input field",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Portal",
     "translation": "",
@@ -9897,6 +9953,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Printer reachable",
+    "translation": "",
+    "context": "Status message when test connection to printer succeeds",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Printers",
     "translation": "",
@@ -10128,6 +10191,20 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Read Full Release Notes",
+    "translation": "",
+    "context": "",
+    "reference": "",
+    "comment": ""
+  },
+  {
+    "term": "Read Full Release Notes",
+    "translation": "",
+    "context": "",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Read:",
     "translation": "",
@@ -12571,6 +12648,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Test Connection",
+    "translation": "",
+    "context": "Button to test connection to a printer by IP address",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Test Page",
     "translation": "",
@@ -12585,6 +12669,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "Testing...",
+    "translation": "",
+    "context": "Button state while testing printer connection",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "Text",
     "translation": "",
@@ -13922,6 +14013,13 @@
     "reference": "",
     "comment": ""
   },
+  {
+    "term": "What's New",
+    "translation": "",
+    "context": "",
+    "reference": "",
+    "comment": ""
+  },
   {
     "term": "When enabled, apps are sorted alphabetically. When disabled, apps are sorted by usage frequency.",
     "translation": "",
@@ -14727,53 +14825,18 @@
     "reference": "",
     "comment": ""
   },
-  {
-    "term": "↑/↓: Navigate • Enter: Paste • Del: Delete • F10: Help",
-    "translation": "",
-    "context": "Keyboard hints when enter-to-paste is enabled",
-    "reference": "",
-    "comment": ""
-  },
-  {
-    "term": "What's New",
-    "translation": "",
-    "context": "",
-    "reference": "",
-    "comment": ""
-  },
-  {
-    "term": "Read Full Release Notes",
-    "translation": "",
-    "context": "",
-    "reference": "",
-    "comment": ""
-  },
-  {
-    "term": "Read Full Release Notes",
-    "translation": "",
-    "context": "",
-    "reference": "",
-    "comment": ""
-  },
-  {
-    "term": "Got It",
-    "translation": "",
-    "context": "",
-    "reference": "",
-    "comment": ""
-  },
-  {
-    "term": "Caps Lock is on",
-    "translation": "",
-    "context": "",
-    "reference": "",
-    "comment": ""
-  },
   {
     "term": "↑/↓: Nav • Space: Expand • Enter: Action/Expand • E: Text",
     "translation": "",
     "context": "",
     "reference": "",
     "comment": ""
+  },
+  {
+    "term": "↑/↓: Navigate • Enter: Paste • Del: Delete • F10: Help",
+    "translation": "",
+    "context": "Keyboard hints when enter-to-paste is enabled",
+    "reference": "",
+    "comment": ""
   }
 ]