[ruanweihong-aaa]

Description

When ai-prompt-guard selects no messages, it returns an empty HTTP 200
without forwarding the request upstream.

PR #14006 fixes this early termination, but embeddings string arrays
still skip inspection because get_messages only extracts string inputs.
For example, with deny_patterns: ["secret"], the batch
{"input": ["secret", "hello"]} would be forwarded without being checked.

This PR:

• Continues request processing when no messages are selected.
• Reuses the existing embeddings text extractor to check all strings in
  a batch, keeping them together so the default last-message filter
  cannot discard earlier items.
• Adds regression tests in a separate file.
• Updates the English and Chinese documentation.

This follows the fix proposed in #14006 and addresses @Baoyuantop's
comments about array inspection and splitting the test file.

Fixes #13944.

Compatibility

No configuration changes are required. String inputs and chat
role/history filtering retain their existing behavior.

Embeddings string arrays now undergo the configured allow/deny checks.
Batch strings are joined with spaces and checked together: allow
patterns apply to the combined text, and any deny-pattern match rejects
the request.

Token-ID arrays are not decoded or inspected. Recognized requests with
no selected text continue processing even with fail_mode: "error",
which applies to unrecognized protocols.

Validation

• New regression tests: 52 assertions pass; the same tests fail
  15 assertions against unmodified master.
• Existing ai-prompt-guard tests: 170 assertions pass.
• Real HTTP tests with a local mock upstream: 23 direct-upstream cases
  and 11 ai-proxy cases pass.
• Changed-file Lua lint, test formatting, and git diff --check pass.
• Full repository CI has not been run.