feat: add cyclomatic complexity reducer agentic workflow

[jamesadevine]

Summary

Adds a daily GitHub Agentic Workflow that identifies and refactors functions with high cyclomatic complexity.

Flow

1. Clippy analysis — runs cargo clippy in JSON mode with clippy::cognitive_complexity enabled
2. Rank & select — picks the highest-complexity function not already processed
3. Refactor — applies extract-helper, flatten-nesting, simplify-logic patterns
4. Verify — runs cargo test + cargo clippy to confirm no regressions
5. Submit PR — creates a PR with before/after complexity scores
6. Cache memory — tracks processed functions across runs to avoid duplicates

Design Decisions

• One function per run — keeps PRs small and reviewable
• Cache memory — prevents re-processing the same function on consecutive runs
• Fallback to manual scan — if Clippy threshold is not exceeded, heuristically finds deeply nested functions
• No behaviour changes — all refactors must preserve existing test outcomes