feat(httpapi): bridge file search endpoints

[kitlangton]

Summary

• Bridge /find, /find/file, and /find/symbol through the experimental Effect HttpApi server.
• Reuse existing file/ripgrep/LSP schemas and mount the search routes behind OPENCODE_EXPERIMENTAL_HTTPAPI.
• Add file HttpApi coverage for text search, file search, and symbol search.

Tests

• bun typecheck from packages/opencode
• bun run test:ci test/server/httpapi-file.test.ts test/server/httpapi-mcp.test.ts test/server/httpapi-workspace.test.ts test/server/httpapi-bridge.test.ts test/server/httpapi-instance.test.ts from packages/opencode
• ./packages/sdk/js/script/build.ts