add middlewares, handlers and database models

internal/db/migrations/00004_create_files_table.sql

@@ -0,0 +1,30 @@
+-- +goose Up
+-- +goose StatementBegin
+CREATE TABLE IF NOT EXISTS files (
+    id TEXT PRIMARY KEY,
+    user_id TEXT NOT NULL,
+    owner_type TEXT NOT NULL,
+    owner_id TEXT NOT NULL,
+    type TEXT NOT NULL,
+    filename TEXT NOT NULL,
+    original_name TEXT,
+    mime_type TEXT,
+    size INTEGER,
+    storage_path TEXT NOT NULL,
+    public BOOLEAN DEFAULT true,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS idx_files_user_id ON files(user_id);
+CREATE INDEX IF NOT EXISTS idx_files_owner ON files(owner_type, owner_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_files_owner_type ON files(owner_type, owner_id, type) WHERE type IN ('avatar');
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+DROP INDEX IF EXISTS idx_files_owner_type;
+DROP INDEX IF EXISTS idx_files_owner;
+DROP INDEX IF EXISTS idx_files_user_id;
+DROP TABLE IF EXISTS files;
+-- +goose StatementEnd