docs: add example programs for common usage patterns

[taigrr]

Fixes #7

Changes

Adds four focused examples in examples/ directory:

• basic — Drop-in logger with web UI, showing package-level functions and log level configuration
• namespaces — Namespace-based logging by component (api, database, auth, cache) with the namespace API endpoint
• client — Programmatic log client with namespace filtering, useful for building custom log processors or alerting
• log-levels — Demonstrates all 8 log levels, formatted variants, and level filtering

Testing

• All examples compile cleanly (go build ./examples/...)
• go vet ./examples/... passes
• Existing tests pass with go test ./... -race