[codex] clarify devdoc rag troubleshooting docs

[shangguanxuan633-lab]

Summary

Clarifies devdoc docs for Open Platform RAG search and API error diagnosis.

Changes

• Defines article search -> search_open_platform_docs_rag.
• Defines error diagnose/troubleshoot -> search_open_error_code_rag, including input priority and parameter mapping.
• Syncs mono/multi skill references, routing docs, README, and command index.

Validation

• git diff --check passed.
• go test ./internal/helpers passed.
• go test ./... run; unrelated baseline/environment failures remain in test/cli_compat, test/scripts, and test/unit.

[shangguanxuan633-lab]

Verified PR head a8cdbf7.

Scope

• Docs-only change across 9 Markdown files.
• Clarifies devdoc routing for Open Platform RAG search and API error diagnosis.
• Aligns mono/multi skill references, skill routing docs, README service summaries, and command index wording.

Passed

• git diff --check
• go test ./internal/helpers

Full Test Run

go test ./... was run but did not pass. The failures appear unrelated to this PR because this change only touches Markdown docs and the failures are in existing fixtures/environment checks:

• test/cli_compat: missing test/cli_compat/testdata/empty_catalog.json, followed by command fixture failures such as no MCP calls captured / unknown command.
• test/scripts: post-goreleaser.sh cannot resolve a package version without DWS_PACKAGE_VERSION or a git tag.
• test/unit: open-source policy check reports an existing marker at internal/app/upgrade_embedded_guard_test.go: EmbeddedMode.

Review Note

Primary review surface is wording and routing accuracy: article search maps to search_open_platform_docs_rag; error diagnose/troubleshoot maps to search_open_error_code_rag; --api, --error-message, and --context are documented as query context rather than standalone MCP parameters.