Documentation overhaul: update README, CLI guide, and add API reference

[ElioNeto]

Problem

The project documentation is significantly outdated and incomplete:

README.md (446 lines)

• Lists only 8 basic REST endpoints
• Missing all 15+ new endpoints: transactions, TTL, range query, batch delete, value search, key search modes, indexes, WebSocket, SSE, Notes
• Quick-start example only shows basic get/set/delete
• No mention of secondary indexes, transactions, or real-time events

docs/CLI_GUIDE.md (509 lines)

• Documents a Portuguese-language REPL that no longer exists
• The actual CLI uses clap subcommands (get/set/delete/scan/keys/count/stats/flush/compact/sql/import/export/token/fixture)
• No mention of any of the new commands
• Examples are in Portuguese and reference different syntax

Missing entirely

• No API reference doc covering all endpoints with request/response schemas
• No Events documentation (WebSocket/SSE)
• No Transaction documentation
• No Secondary Index documentation
• No Notes documentation (12+ endpoints)
• No upgrade/migration guide from v2.1.x to v2.2.0

Request

1. Update README.md:

   • Complete endpoint table with all HTTP endpoints
   • Add sections for: Transactions, TTL, Pagination, Range Queries, Search, Indexes, Events, Notes
   • Update quick-start to show more features
   • Add links to detailed docs

2. Rewrite docs/CLI_GUIDE.md:

   • Document all actual clap subcommands
   • Add examples for new commands
   • Keep examples in English (consistent with codebase)
   • Add --help output for each command group

3. Create docs/API_REFERENCE.md:

   • Complete REST API reference with all endpoints
   • Request/response schemas
   • Status codes and error responses
   • Authentication requirements per endpoint
   • Pagination, filtering, and cursor semantics

4. Create docs/EVENTS.md:

   • WebSocket and SSE protocol documentation
   • Event payload format
   • Filtering options
   • Reconnection and backpressure semantics

Acceptance criteria

• README.md accurately reflects all v2.2.0 features
• CLI_GUIDE.md documents the actual CLI, not the old REPL
• New docs follow existing doc style
• All API endpoints are documented with examples