Set Kemal max_request_line_size to 16384 for large channel continuation query parameters. (#5566)

* feat: Add configurable max_request_line_size to handle long URLs

This commit adds a new configuration option `max_request_line_size` that allows
users to increase the HTTP request line size limit. This is particularly useful
for handling very long continuation tokens that can cause 414 (URI Too Long) errors.

Changes:
- Add `max_request_line_size` property to Config class
- Configure Kemal server to use the custom limit if specified
- Document the option in config.example.yml with recommendations
- Add examples in docker-compose.yml for both YAML and env var configuration

The default behavior remains unchanged (8KB limit) unless explicitly configured.
This provides a solution for users experiencing 414 errors without affecting
existing installations.

* Hardcode max_request_line_size to 16384

---------

Co-authored-by: Sunghyun Kim <hello@sunghyun.me>

src/invidious.cr

@@ -250,6 +250,8 @@ Kemal.config.app_name = "Invidious"
 {% end %}
 
 Kemal.run do |config|
+  config.server.not_nil!.max_request_line_size = 16384
+
   if socket_binding = CONFIG.socket_binding
     File.delete?(socket_binding.path)
     # Create a socket and set its desired permissions