perf(registry): opt-in compression for JSON API responses

[ricardo-devis-agullo]

Problem: middleware/compression.ts only serves the pre-compressed oc-client static file (routes/static-redirector.ts). Batch POST / and discovery JSON responses - the largest payloads the registry serves - go out uncompressed (item 5, registry-performance-improvements.md).

Change: new opt-in registry option compression (boolean, default OFF so CDN-terminated deployments pay nothing).

• Express adapter gains enableCompression() (standard compression() middleware, default 1KB threshold, gzip/deflate); wired in middleware.bind only when options.compression is true.
• Option plumbed through options-sanitiser (defaults false) with JSDoc on Config.compression; adapter interface extended with optional enableCompression? so third-party adapters keep compiling.
• Fastify: NOT mirrored - left as follow-up. @fastify/compress would need a new dependency plus adapter plumbing and parity testing; the optional interface method is the seam for it.

Verify:

• New spec test/unit/registry-middleware-compression.js (6 tests): sanitiser defaults false/preserves true; JSON route returns identity with option off despite Accept-Encoding: gzip; gzip Content-Encoding + gunzip round-trip with option on; deflate round-trip; identity with no Accept-Encoding.
• Payload sizes (100-component JSON fixture, 32906 bytes uncompressed): off -> identity 32906 for gzip/deflate/identity; on -> gzip 509 bytes (~65x), deflate 497 bytes, identity 32906.
• Full packages/oc suite (npm run test-silent): 1103 passing, 0 failing.
• Did NOT touch routes/index.ts, domain/repository.ts, version-handler.