feat: add fast declarative project detection - #20

Adds brainpod detect [path] --json to discover projects, language/toolchain declarations, frameworks, runtimes, and workspaces across nine languages and mixed monorepos, including Deno/npm/pnpm layouts, with source evidence and provider/consumer roles.

• Compiled TOML rules/catalog drive discovery, fact extraction, version mappings, and workspace policy. Format adapters handle JSONC, imports, and local build metadata without executing project code or installing dependencies.
• Bounded, deterministic scanning reads manifests—not application source bodies. Deno runtime versions stay separate from language/package versions; mixed registries retain dependency declarations and manager-specific workspace membership.
• Includes 51 pinned public repositories (45 original, five ranked Deno projects, one mixed-workspace supplement), plus all ten Brainpod starter branches. Repository lists and rerun commands are in README and tests/detect-corpus.md.

Validated locally: 295/295 corpus assertions, 195 Rust tests, 11 audit-runner tests, Clippy/formatting, and offline all-platform flake evaluation. Warm scan benchmark: ~4.5 ms for 20,200 files with 200 manifest reads; these are local measurements, not latency guarantees.