Support Reverse Proxy and SSL Protocol Detection

[alcayaga]

Fixes #46

Summary

Adds support for running the local audio server behind a reverse proxy, specifically addressing issues with hardcoded binding and static URL generation in responses.

Changes

• Configurable Binding: Added host and port settings to default_config.json. This allows users to change the binding from
  127.0.0.1 to 0.0.0.0 for external access while keeping the secure default for most users.
• Dynamic Host & Protocol Detection:
  • The server now uses the Host header from incoming requests to build audio URLs.
  • It now detects the X-Forwarded-Proto header (commonly sent by proxies like Nginx) to determine if http or https should be used in the response.
• Configuration Refactor: Centralized configuration management in plugin/config.py by removing hardcoded constants from plugin/consts.py and using a shared CONFIG object across the project.

Motivation

Previously, the server was hardcoded to bind to 127.0.0.1, and all audio URLs returned to Yomitan were hardcoded to http://127.0.0.1:5050. This made it impossible to use the server over a network or behind a proxy with SSL, as the client would receive unreachable local links.

How to Test

1. Local default: Run the server normally. It should still bind to 127.0.0.1:5050 and return http links.
2. Reverse Proxy simulation:
   • Set "host": "0.0.0.0" in config.json.
   • Send a request with proxy headers:
     curl -H "Host: my-proxy.net" -H "X-Forwarded-Proto: https" "http://localhost:5050/?term=読む"
   • Verify that the url fields in the JSON response start with https://my-proxy.net/.