refactor: adopt portigo infrastructure patterns

Add config package with build-tag-switched dev/prod environments,
structured logging via zerolog, Taskfile for dev workflow, golangci-lint
config, testutil package, and improved DB setup with proper SQLite
pragmas and cleanup. Rename sqlc output package from gen to repository.

Switch to allowlist .gitignore, Alpine+UPX+scratch Dockerfile, and
CI pipeline with test/lint gates before deploy.

.env.example

@@ -1,5 +1,16 @@
-# Application URL for invite links (defaults to https://games.adriatica.io)
+# Log level (TRACE, DEBUG, INFO, WARN, ERROR). Defaults to INFO.
+# LOG_LEVEL=DEBUG
+
+# SQLite database path. Defaults to data/c4.db.
+# DB_PATH=data/c4.db
+
+# Application URL for invite links. Defaults to https://games.adriatica.io.
 # APP_URL=http://localhost:7331
 
-# Server port (defaults to 7331)
+# Server port. Defaults to 7331.
 # PORT=7331
+
+# Goose CLI migration config (only needed for running goose manually)
+GOOSE_DRIVER=sqlite3
+GOOSE_DBSTRING=data/c4.db?_pragma=foreign_keys(1)&_pragma=journal_mode(WAL)
+GOOSE_MIGRATION_DIR=db/migrations