License the project; add root README, website, and parked release CI

- Code: GPL-3.0-or-later (LICENSE, SPDX headers on all .kt/.aidl).
  Specs in docs/: CC-BY-4.0 (docs/LICENSE). Rationale in build-status.md;
  server decided GPL (not AGPL).
- Root README for the public repo.
- web/: Cloudflare Worker site for echo-lot.app. /apk resolves the newest
  APK from the Gitea latest-release API at request time (edge-cached 5 min),
  so tagging a release is the only publish step. /fdroid, /source, and a
  manual DOWNLOAD_URL fallback are wrangler vars.
- .gitea/workflows/release.yml: tag-driven (v*) signed semver APK builds for
  the future production app in echolot-app/. Parked; the prober is
  deliberately not CI-built.
- Fix UserService.kt: drop the explicit secondary constructor that
  conflicted with the implicit primary (never compiled before — first
  local build caught it). Prober now builds: :app:assembleDebug OK.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

echolot-prober/app/src/main/aidl/app/echo_lot/prober/shizuku/IUserService.aidl

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // IUserService.aidl
 package app.echo_lot.prober.shizuku;
 

echolot-prober/app/src/main/java/app/echo_lot/prober/MainActivity.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober
 
 import android.Manifest

echolot-prober/app/src/main/java/app/echo_lot/prober/export/Report.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.export
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/BleAdvertiseProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.bluetooth.BluetoothManager

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/ErrqueueProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/IcmpProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/LinkPropertiesProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/MultiNetworkProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/MulticastProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/OsAbi.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.system.Os

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/Probe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/ProbeRegistry.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 /** All probes the app runs, in display order. */

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/ShizukuProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/probe/SockOptProbe.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.probe
 
 import android.content.Context

echolot-prober/app/src/main/java/app/echo_lot/prober/shizuku/ShizukuRunner.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.shizuku
 
 import android.content.ComponentName

echolot-prober/app/src/main/java/app/echo_lot/prober/shizuku/UserService.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.shizuku
 
 import kotlin.system.exitProcess
@@ -11,9 +14,7 @@ import kotlin.system.exitProcess
  * implementing the AIDL Stub.
  */
 class UserService : IUserService.Stub() {
-
-    // Required no-arg constructor for Shizuku UserService.
-    constructor()
+    // The implicit no-arg primary constructor is the one Shizuku requires.
 
     override fun destroy() {
         exitProcess(0)

echolot-prober/app/src/main/java/app/echo_lot/prober/ui/ProberScreen.kt

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package app.echo_lot.prober.ui
 
 import androidx.compose.foundation.layout.Arrangement