refactor: reorganize project structure and update configurations

- Move migrations/ to database/schema/ for clarity on database schema definitions
- Move sqlc.yaml to internal/database/ to group with database code
- Move static/ to cmd/server/static/ to co-locate with server
- Update all configuration files and documentation
- Follow Go project conventions for better organization

database/schema/003_add_ebook_metadata_fields.up.sql

@@ -0,0 +1,8 @@
+-- Add additional metadata fields to ebooks table
+ALTER TABLE ebooks ADD COLUMN series VARCHAR(255);
+ALTER TABLE ebooks ADD COLUMN series_number INTEGER;
+ALTER TABLE ebooks ADD COLUMN tags TEXT;
+ALTER TABLE ebooks ADD COLUMN asin VARCHAR(20);
+ALTER TABLE ebooks ADD COLUMN date_published DATE;
+ALTER TABLE ebooks ADD COLUMN publisher VARCHAR(255);
+ALTER TABLE ebooks ADD COLUMN contributors TEXT;