fix: align PHP RPC namespaces and response handler

[tolga-tom-nook]

Summary

• aligns Composer package metadata and PSR-4 autoloading with the repository's naftalimurgor\Bitgesell namespaces
• moves Config out of the stale Denpa\Bitcoin namespace and updates the client config provider
• fixes the response handler/class mismatch (BitgeselldResponse typo vs BitcoindResponse file/tests)
• replaces the stale duplicated Go README with PHP Bitgesell Core RPC usage notes

Validation

• python3 -m json.tool composer.json
• static scan confirmed no remaining Denpa\Bitcoin, BitgeselldResponse, denpa/php-bitcoinrpc, or stale Go README references
• git diff --check

Notes

PHP/Composer are not installed in this runner, so runtime PHPUnit execution was not available here. The changed symbols are direct namespace/class-string mismatches that would otherwise break Composer autoloading and response wrapping.

[MyTH-zyxeon]

Maintainer review note for the #81/denpamusic#39 bounty queue:

I checked head 7503244: this is broader than a docs cleanup, but the core implementation surface is specific and reviewable: Composer metadata/PSR-4 namespaces move from Denpa\Bitcoin to naftalimurgor\Bitgesell, and Client::getResponseHandler() now points at the actual BitcoindResponse class name instead of the stale BitgeselldResponse spelling.

Acceptance checks:

• Run composer dump-autoload and the existing PHPUnit suite so the renamed PSR-4 app/test namespaces resolve without relying on stale classmap state.
• Confirm all PHP source files under src/ already use or import naftalimurgor\Bitgesell consistently; any remaining Denpa\Bitcoin references should be intentional compatibility aliases, not leftovers.
• Exercise one basic JSON-RPC response path so Client::getResponseHandler() instantiates Responses\BitcoindResponse successfully.
• Review README separately from the code changes because it deletes a large stale Go-oriented section; the docs rewrite should not hide any runtime behavior change.

No wallet/key/node/live-chain scope; this is namespace/autoload/response-handler hygiene only.