docs: add Equibles MCP server example

[daniel3303]

Summary

Adds an Equibles MCP server example to the mcpServers tabs in docs/config/tools.md, after the FXMacroData one (#636). Docs only, no code changes.

Equibles is a remote MCP server at https://mcp.equibles.com/mcp with US stock market data: SEC filing search, XBRL financial statements, earnings call transcripts, insider and congressional trades and 13F holdings. Tool calls need either OAuth or an API key sent as Authorization: Bearer <key>, so the tab has two configs:

• OAuth: https://mcp.equibles.com/mcp?auth=oauth. Without the parameter the server answers initialize and tools/list anonymously, so ECA would start the server with all tools and only fail at the first call. With it, initialize returns 401 plus WWW-Authenticate: Bearer resource_metadata=..., and ECA goes through DCR and shows the server as requires-auth until the user signs in.
• API key: the static header from EQUIBLES_API_KEY, which skips the OAuth probe like the "Static auth header" example.

Validation

I ran the released eca-native-macos-aarch64 0.163.0 binary (SHA-256 checked against the release) as eca server --config-file with each config block extracted verbatim, under a scratch HOME, and drove initialize/initialized over stdio:

• OAuth config: [OAUTH] DCR succeeded at https://equibles.com/connect/register, then MCP server 'equibles' requires authentication, and tool/serverUpdated reports requires-auth. I did not complete the browser sign-in from the test harness.

• API-key config, with EQUIBLES_API_KEY unset: Started MCP server equibles, and tool/serverUpdated reports running with 117 tools (SearchDocuments, GetFinancialStatement, GetInsiderTransactions, ...). Tool calls return 401 until a key is set.

• I added a entry in changelog under unreleased section. (Docs-only, like docs: add Serply MCP server example #626 and docs: add FXMacroData MCP server example #636, so I left CHANGELOG.md alone. Happy to add a line if you want one.)

• This is not an AI slop.

AI tools helped draft this; I reviewed and tested it. Happy to adjust naming or scope, or drop it if it isn't a direction you want for the docs.

Disclosure: I build Equibles.