github: switch issue-labeller to bot webhook and add configuration

Remove the standalone GitHub Actions issue-labeller.yml workflow in favor
of the webhook-based openwrt-bot worker.

Enable issue labeller in formalities.json and add a declarative
.github/issue-labeller.yml configuration file for automated validation
and labelling of bug reports (release, target, image kind, device).

The release rule lists two alternative conditions under a single label
key: concrete releases (x.y.z, x.y.z-rcN) are validated against their
Git tag via exists check, while stable-branch snapshots (x.y-SNAPSHOT)
are format-validated only — OpenWrt does not tag snapshot builds.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24382
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

.github/formalities.json

@@ -25,5 +25,6 @@
   "check_pkg_release": "warning",
   "require_linked_github_account": "warning",
   "enable_stale_bot": false,
-  "enable_labeler_yml": true
+  "enable_labeler_yml": true,
+  "enable_issue_labeller": true
 }

.github/issue-labeller.yml

@@ -0,0 +1,43 @@
+# Configuration for OpenWrt Issue Labeller
+# Automates issue form validation and labelling via openwrt-bot webhook.
+
+_trigger_label: "to-triage"
+_invalid_label: "invalid"
+_remove_labels: ["to-triage"]
+_invalid_comment: "Invalid {field} reported. `{value}`"
+
+# Tag release branch (e.g. release/23.05 or release/24.10).
+# The list items are alternatives: concrete releases (24.10.7, 25.12.0-rc2)
+# must have a matching Git tag, while stable-branch snapshots (24.10-SNAPSHOT)
+# are format-validated only — OpenWrt does not tag snapshot builds.
+"release/{major}.{minor}":
+  - field: "release"
+    format: '^\d+\.\d+\.\d+(-rc\d+)*$'
+    exists: "tag:v{value}"
+  - field: "release"
+    format: '^\d+\.\d+-SNAPSHOT$'
+
+# Tag development snapshot release
+"SNAPSHOT":
+  - field: "release"
+    format: '^SNAPSHOT$'
+
+# Tag target (e.g. target/x86, target/ath79, target/ramips)
+"target/{segment0}":
+  - field: "target"
+    format: '^[a-zA-Z0-9]+/[a-zA-Z0-9]+$'
+    exists: "path:target/linux/{segment0}/{segment1}"
+
+# Tag image source
+"Official Image":
+  - field: "image_kind"
+    contains: "official"
+
+"Self Built Image":
+  - field: "image_kind"
+    contains: "self"
+
+# Tag supported device
+"Supported Device":
+  - field: "device"
+    not_empty: true

.github/workflows/issue-labeller.yml

@@ -1,11 +0,0 @@
-name: Issue Labeller
-on:
-  issues:
-    types: [ opened ]
-
-jobs:
-  label-component:
-    name: Validate and Tag Bug Report
-    permissions:
-      issues: write
-    uses: openwrt/actions-shared-workflows/.github/workflows/issue-labeller.yml@main