docs: improve README for SEO and discoverability

Add badges (CI, npm, crates.io, license), table of contents, and a
comparison table replacing the bullet list. Distribute keywords
throughout (local log aggregator, Rust CLI, Docker log viewer, TUI,
monorepo, SSE, npx). Add tech stack table in Architecture and a
Contributing section with the local quality gate commands.

Author: akosidencio