Add API documentation and underground station importer

- Introduced a new HTML documentation page for the oradio API, including a JavaScript file to handle dynamic content and API requests.
- Added a CSS file for styling the documentation page.
- Implemented an underground station importer script that fetches data from Radio-Browser and writes it to a JSON file.
- Created a stats module to compute and manage vote and play statistics for radio stations.
- Added a polyfill for modulepreload to ensure compatibility with older browsers.

server/db/schema.sql

@@ -78,3 +78,23 @@ CREATE TABLE IF NOT EXISTS play_history (
 );
 
 CREATE INDEX IF NOT EXISTS idx_history_user ON play_history(user_id, started_at DESC);
+CREATE INDEX IF NOT EXISTS idx_history_station ON play_history(station_id);
+
+-- One vote per user per station. value is +1 (up) or -1 (down). Row is
+-- deleted entirely when the user clears their vote, so the COUNT is exact.
+CREATE TABLE IF NOT EXISTS station_votes (
+  user_id    INTEGER NOT NULL REFERENCES users(id)    ON DELETE CASCADE,
+  station_id INTEGER NOT NULL REFERENCES stations(id) ON DELETE CASCADE,
+  value      INTEGER NOT NULL CHECK (value IN (-1, 1)),
+  created_at TEXT    NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  PRIMARY KEY (user_id, station_id)
+);
+CREATE INDEX IF NOT EXISTS idx_votes_station ON station_votes(station_id);
+
+-- Aggregate play counter. Cheaper than COUNT(*) over play_history every render
+-- and lets anonymous/public listing show play counts without exposing history.
+CREATE TABLE IF NOT EXISTS station_plays (
+  station_id     INTEGER PRIMARY KEY REFERENCES stations(id) ON DELETE CASCADE,
+  plays          INTEGER NOT NULL DEFAULT 0,
+  last_played_at TEXT
+);