Feature/deploy

[Howard-nolan]

Change Summary:

• Added DB_PATH and BASE_URL config plumbing; handlers now build short URLs from BASE_URL and routes drop /v1 in favor of /shorten and /r/{code}.
• Swapped SQLite driver to modernc.org/sqlite for CGO‑free static builds; added multi‑stage distroless Dockerfile, .dockerignore, and an app service + volume in docker-compose.yml.
• Updated tests, OpenAPI, README, Prometheus config, and LEARNINGS to match the new paths and metrics endpoint.

How It Works:

• config.Load() reads PORT, DB_PATH, and BASE_URL; main opens SQLite with db.OpenAndMigrate(cfg.DbPath) and passes cfg.BaseURL into the handler.
• Handler trims the base URL; ShortenHandler inserts a link and returns ${BASE_URL}/r/{code}, while /r/{code} redirects to the original URL; /metrics exposes Prometheus text format.
• Docker build compiles a static binary with CGO_ENABLED=0 and runs it on distroless; compose wires env vars and mounts a named volume for persistent SQLite.

Additional Notes (optional):

• Default DB_PATH is app.db; compose overrides it to app.db for persistence—Cloud Run will need an explicit DB_PATH or a durable datastore.
• OpenAPI/README examples now use /shorten, /r/{code}, and /metrics.