feat: add servicelink RPC mesh endpoint

- Add the servicelink submodule and register POST /rpc for node-to-node file operations.
- Require bearer tokens with the mesh scope and apply rate/body-size limits to RPC calls.
- Map database connectivity failures to the existing 504 database error flow, with JSON responses for API routes.
- Cover the new RPC handlers and database error handling with focused pytest tests.
- Bump the NanoShare package version to 1.21.0.

routes/handeling/errorsAndBots.py

@@ -13,6 +13,7 @@ from my_modules.functions import (
 )
 from quart_common.web.env import is_development_environment
 from quart_common.web.wide_event import add_wide_event_context
+import httpx
 
 IGNORED_404_PATHS = [
   "/.well-known/",
@@ -186,6 +187,11 @@ async def internal_server_error(e):
     file={'name': '500.webp', 'alt': "Astronaut jumping and clicking on random Buttons as a red alert gone off - They is a Text on the Image saying: Why don't shit Work!?!"},
   ), 500
 
+@app.errorhandler(httpx.HTTPError)
+@app.errorhandler(TimeoutError)
+async def database_unavailable_error(e):
+  return await database_server_error(e)
+
 @app.errorhandler(504)
 async def database_server_error(e):
   try:
@@ -193,8 +199,12 @@ async def database_server_error(e):
   except LookupError as e:
     return await to_many_requests(e)
 
+  context = get_request_context()
   add_wide_event_context(error={"type": type(e).__name__, "message": str(e)})
   logger.error(e)
+  if context.path.startswith("/api"):
+    return jsonify({"error": "Database Error", "message": "The database is currently unavailable. Please try again in a moment."}), 504
+
   return await render_template('views/basics/error.htm',
     title='Database Error',
     header={'title': '504 - Database Error', 'message': "It looks like something is broke on our end... but don't worry, we're fixing it! Either way, thanks for helping us find new ways to crash our system. Stay curious, hacker-friend!"},