docs: relicense Sencho to AGPLv3 and reframe Community positioning (#1623)

* docs: relicense Sencho to AGPLv3 and reframe Community positioning

Replace BSL with AGPLv3 for the public Community product, update contributor
and licensing copy for Community-focused contributions, and surface source
and license links in Settings About.

* docs: clarify CLA scope and Community contribution framing

* fix(ui): split About link constants and harden AboutSection test selectors

backend/package-lock.json

@@ -8,7 +8,7 @@
       "name": "backend",
       "version": "1.0.0",
       "hasInstallScript": true,
-      "license": "SEE LICENSE IN LICENSE",
+      "license": "AGPL-3.0-only",
       "dependencies": {
         "axios": "^1.15.0",
         "bcrypt": "^6.0.0",

backend/package.json

@@ -23,7 +23,7 @@
   },
   "keywords": [],
   "author": "",
-  "license": "SEE LICENSE IN LICENSE",
+  "license": "AGPL-3.0-only",
   "type": "commonjs",
   "engines": {
     "node": ">=26.0.0"