fix: pass claude cli thinking effort (#77410)

Summary:
- Adds a plugin-owned CLI backend argument rewrite hook and wires Anthropic `claude-cli` to translate non-off `/think` levels into Claude Code `--effort`, with docs, changelog, API baseline, and tests.
- Reproducibility: yes. Current main has a high-confidence source reproduction: choose `claude-cli`, set a non ... builds argv from backend args that contain no `--effort` even though `thinkLevel` exists on the run params.

Automerge notes:
- No ClawSweeper repair was needed after automerge opt-in.

Validation:
- ClawSweeper review passed for head be17754009.
- Required merge gates passed before the squash merge.

Prepared head SHA: be17754009
Review: https://github.com/openclaw/openclaw/pull/77410#issuecomment-4372812685

Co-authored-by: stainlu <stainlu@newtype-ai.org>

docs/tools/thinking.md

@@ -54,6 +54,7 @@ title: "Thinking levels"
 ## Application by agent
 
 - **Embedded Pi**: the resolved level is passed to the in-process Pi agent runtime.
+- **Claude CLI backend**: non-off levels are passed to Claude Code as `--effort` when using `claude-cli`; see [CLI backends](/gateway/cli-backends).
 
 ## Fast mode (/fast)