feat(examples/actors/code_review.yaml): add a new code review tool (#458)

## Summary

Add a `code_review.yaml` actor example that uses Claude Opus 4 with file and git tools to perform automated code reviews against the project's review playbook.

### Changes
- **New file**: `examples/actors/code_review.yaml` — LLM actor configured with `files/read_file`, `files/list_directory`, and `builtin/git-*` tools, with a system prompt that reads `docs/development/review-playbook.md` and diffs against `master`
- **Updated**: `features/actor_examples.feature` — bumped example count from 7 to 8 and added `code_review.yaml` to the file listing assertion

### Verification
- `nox -e lint` — passed
- `nox -e typecheck` — 0 errors
- `nox -e format -- --check` — all files formatted
- `nox -s unit_tests -- features/actor_examples.feature` — 25 scenarios passed

### Rebase Notes
- Rebased onto current master (`4d3499dc`)
- Squashed 2 commits into 1 (eliminated 3 merge commits)
- Resolved conflict in `actor_examples.feature`: master added `strategy_with_subplan.yaml` (count 7), our branch adds `code_review.yaml` (count now 8)

Reviewed-on: #458
Reviewed-by: Jeffrey Phillips Freeman <jeffrey.freeman@cleverthis.com>
Co-authored-by: Brent Edwards <brent.edwards@cleverthis.com>
Co-committed-by: Brent Edwards <brent.edwards@cleverthis.com>

examples/actors/code_review.yaml

@@ -0,0 +1,46 @@
+# LLM Actor - Code Review
+# Runs a multi-step code review.
+
+name: local/code-review
+type: llm
+description: Runs a code review and merges to make the best possible.
+version: "0.0"
+
+# LLM model form is Claude Opus 4
+model: claude-opus-4-20250514
+
+system_prompt: |
+    You are a code reviewer.
+
+    Use the tool `files/read_file` to read the instructions at `docs/development/review-playbook.md`.
+
+    Then use the tool `builtin/git-diff` to compare the current state of this code base against
+    the `master` branch of the code base.
+
+    Use your deep knowledge of testing, test flaws, performance, bug detection, and
+    security issues to find any possible problems in the code.
+
+    Create a report that summarizes all found problems.
+
+tools:
+    - files/read_file
+    - files/list_directory
+    - builtin/git-status
+    - builtin/git-diff
+    - builtin/git-log
+    - builtin/git-blame
+
+# Context settings
+context_view: executor
+memory:
+    enabled: true
+    max_messages: 30
+    max_tokens: 6000
+
+context:
+    max_context_tokens: 16000
+
+# Environment variables
+env_vars:
+    WORK_DIR: ${HOME}
+    LOG_LEVEL: info