refactor(core): replace JSON-based pipeline with MySQL database

This commit introduces a major architectural overhaul, migrating the data backend from a flat JSON
file to a relational MySQL database.

- Replaced multiple scraping scripts with a unified `main.py` that handles crawling, parsing, and
database synchronization.
- Introduced `mysql_helper.py` for robust database interaction with a connection pool.
- Added `queries.sql` defining the new database schema for assets, categories, tags, and changelogs.
- Removed all obsolete frontend code (v1, v2) and old scraping scripts.

This change provides a more scalable and maintainable foundation for managing asset data.

queries.sql

@@ -0,0 +1,73 @@
+SET FOREIGN_KEY_CHECKS = 0;
+DROP TABLE IF EXISTS category;
+DROP TABLE IF EXISTS series;
+DROP TABLE IF EXISTS tag;
+DROP TABLE IF EXISTS asset_pack;
+DROP TABLE IF EXISTS asset_pack_image;
+DROP TABLE IF EXISTS asset_pack_tag;
+DROP TABLE IF EXISTS update_log;
+SET FOREIGN_KEY_CHECKS = 1;
+
+CREATE TABLE category (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  name VARCHAR(100) NOT NULL UNIQUE
+);
+
+CREATE TABLE series (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  name VARCHAR(100) NOT NULL UNIQUE
+);
+
+CREATE TABLE tag (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  name VARCHAR(100) NOT NULL UNIQUE
+);
+
+CREATE TABLE asset_pack (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  name VARCHAR(255) NOT NULL UNIQUE,
+  category_id INT NOT NULL,
+  series_id INT,
+  discovered_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+  released_at DATE,
+  updated_at DATE,
+  base_asset_path VARCHAR(255),
+  orig_page_link VARCHAR(255),
+  FOREIGN KEY (category_id) REFERENCES category(id) ON DELETE RESTRICT ON UPDATE CASCADE,
+  FOREIGN KEY (series_id) REFERENCES series(id) ON DELETE SET NULL ON UPDATE CASCADE,
+  INDEX idx_name (name),
+  INDEX idx_category (category_id),
+  INDEX idx_series (series_id)
+);
+
+CREATE TABLE asset_pack_image (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  asset_pack_id INT NOT NULL,
+  image_file_name VARCHAR(255),
+  orig_file_link VARCHAR(255),
+  FOREIGN KEY (asset_pack_id) REFERENCES asset_pack(id) ON DELETE CASCADE,
+  INDEX idx_asset_pack_id (asset_pack_id)
+);
+
+CREATE TABLE asset_pack_tag (
+  asset_pack_id INT NOT NULL,
+  tag_id INT NOT NULL,
+  PRIMARY KEY (asset_pack_id, tag_id),
+  FOREIGN KEY (asset_pack_id) REFERENCES asset_pack(id) ON DELETE CASCADE,
+  FOREIGN KEY (tag_id) REFERENCES tag(id) ON DELETE CASCADE
+);
+
+CREATE TABLE update_log (
+  id INT PRIMARY KEY AUTO_INCREMENT,
+  asset_pack_id INT NOT NULL,
+  released_date DATE NOT NULL,
+  version VARCHAR(20),
+  description VARCHAR(500),
+  files_count INT UNSIGNED DEFAULT 0,
+  feat_animations TINYINT(1) DEFAULT 0,
+  feat_variations TINYINT(1) DEFAULT 0,
+  zip_file_name VARCHAR(255),
+  orig_download_link VARCHAR(255),
+  FOREIGN KEY (asset_pack_id) REFERENCES asset_pack(id) ON DELETE CASCADE,
+  INDEX idx_released_date (released_date)
+);