Get the repo ready for F-Droid

- License: AGPL-3.0-or-later (LICENSE, every package.json, README).
- MUSICSHARE_FOSS=1 builds leave out the only closed-source code, Google's
  ML Kit / Play Services barcode scanner bundled by expo-camera; the scan
  screen then decodes small camera snapshots with jsQR instead.
- Expo modules build from source rather than from precompiled AARs, as
  F-Droid requires (that's also what makes the scanner switch take effect).
  Verified: a FOSS build contains no ML Kit or Play Services classes.
- Release builds default to the production server, and come out unsigned
  without our upload key (F-Droid signs with its own). versionCode 1.
- Store listing in fastlane/metadata/android, a draft fdroiddata recipe in
  fdroid/, and docs/FDROID.md with the submission steps.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

package-lock.json

@@ -829,6 +829,8 @@
         "expo-symbols": "~57.0.3",
         "expo-system-ui": "~57.0.4",
         "expo-web-browser": "~57.0.3",
+        "jpeg-js": "^0.4.4",
+        "jsqr": "^1.4.0",
         "react": "19.2.3",
         "react-dom": "19.2.3",
         "react-native": "0.86.3",
@@ -13232,6 +13234,12 @@
         "node": ">=10"
       }
     },
+    "node_modules/jpeg-js": {
+      "version": "0.4.4",
+      "resolved": "https://registry.npmjs.org/jpeg-js/-/jpeg-js-0.4.4.tgz",
+      "integrity": "sha512-WZzeDOEtTOBK4Mdsar0IqEU5sMr3vSV2RqkAIzUEV2BHnUfKGyswWFPFwK5EeDo93K3FohSHbLAjj0s1Wzd+dg==",
+      "license": "BSD-3-Clause"
+    },
     "node_modules/js-tokens": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/js-tokens/-/js-tokens-4.0.0.tgz",
@@ -13329,6 +13337,12 @@
         "node": ">=6"
       }
     },
+    "node_modules/jsqr": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/jsqr/-/jsqr-1.4.0.tgz",
+      "integrity": "sha512-dxLob7q65Xg2DvstYkRpkYtmKm2sPJ9oFhrhmudT1dZvNFFTlroai3AWSpLey/w5vMcLBXRgOJsbXpdN9HzU/A==",
+      "license": "Apache-2.0"
+    },
     "node_modules/jsx-ast-utils": {
       "version": "3.3.5",
       "resolved": "https://registry.npmjs.org/jsx-ast-utils/-/jsx-ast-utils-3.3.5.tgz",