Relicense project under GPL-3.0-or-later

Replaces the previous MIT license with GPL-3.0-or-later. Adds the full
GPL-3.0 license text at LICENSE, updates pyproject.toml metadata and
classifier, updates the README, and adds SPDX-License-Identifier headers
to all first-party server Python and client JavaScript sources.
Third-party anime.min.js is left untouched.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/admin.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 /**
  * Golf Admin Dashboard
  * JavaScript for admin interface functionality

client/animation-queue.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // AnimationQueue - Sequences card animations properly
 // Ensures animations play in order without overlap
 

client/app.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // Golf Card Game - Client Application
 
 // Debug logging - set to true to see detailed state/animation logs

client/card-animations.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // CardAnimations - Unified anime.js-based animation system
 // Replaces draw-animations.js and handles ALL card animations
 

client/card-manager.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // CardManager - Manages persistent card DOM elements
 // Cards are REAL elements that exist in ONE place and move between locations
 

client/leaderboard.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 /**
  * Leaderboard component for Golf game.
  * Handles leaderboard display, metric switching, and player stats modal.

client/replay.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // Golf Card Game - Replay Viewer
 
 class ReplayViewer {

client/state-differ.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // StateDiffer - Detects what changed between game states
 // Generates movement instructions for the animation queue
 

client/timing-config.js

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 // Centralized timing configuration for all animations and pauses
 // Edit these values to tune the feel of card animations and CPU gameplay