Add Navidrome Scrobbled scrobbler plugin

A Python Extism plugin for Navidrome that scrobbles playback to a
self-hosted Scrobbled (Last.fm-compatible) server, plus Gitea Actions
CI that lints, tests, builds/validates, and publishes the .ndp
artifact to pkgs.daubney.dev.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018n5ffHCn5QUjpDtuWTk3fh

tests/stubs/extism.py

@@ -0,0 +1,54 @@
+"""Minimal fake `extism` module for testing plugin/__init__.py's pure business
+logic under plain CPython, without the real extism-py/wasm runtime.
+
+Never shipped or compiled - only used by tests/test_logic.py, which puts this
+directory at the front of sys.path before importing the plugin module.
+"""
+
+
+def import_fn(namespace, name):
+    def decorator(fn):
+        return fn
+
+    return decorator
+
+
+def plugin_fn(fn):
+    return fn
+
+
+class LogLevel:
+    Info = "info"
+    Error = "error"
+
+
+def log(level, message):
+    pass
+
+
+class Config:
+    @staticmethod
+    def get_str(key):
+        return None
+
+
+def input_json():
+    return {}
+
+
+def output_str(value):
+    pass
+
+
+class _Memory:
+    def alloc(self, data):
+        raise NotImplementedError("host memory is not available in tests")
+
+    def find(self, offset):
+        raise NotImplementedError("host memory is not available in tests")
+
+    def string(self, mem):
+        raise NotImplementedError("host memory is not available in tests")
+
+
+memory = _Memory()