feat(auth): enhance middleware to support Bearer token auth

* Added support for extracting Bearer tokens from Authorization header.
* Updated middleware to prefer explicit header over Bearer token.
* Improved test coverage for authentication scenarios.

README.md

@@ -47,7 +47,7 @@ A Go MCP server for capturing and retrieving thoughts, memory, and project conte
 Config is YAML-driven. Copy `configs/config.example.yaml` and set:
 
 - `database.url` — Postgres connection string
-- `auth.keys` — API keys for MCP endpoint access
+- `auth.keys` — API keys for MCP endpoint access via `x-brain-key` or `Authorization: Bearer <key>`
 - `ai.litellm.base_url` and `ai.litellm.api_key` — LiteLLM proxy
 - `ai.ollama.base_url` and `ai.ollama.api_key` — Ollama local or remote server