test: add unit tests for `optimization/`

[KRRT7]

Parent: #2079

Phase 1 — Optimization orchestrator

Module	Stmts	Current coverage
optimization/	496	25%

Key file:

• optimization/optimizer.py (496 stmts, 25%) — main optimization pipeline orchestration

This is the core orchestrator. Test each stage of the pipeline in isolation: function preparation, candidate generation dispatch, verification flow, and result handling. Mock the AI service and test runners.

Target

100% coverage for optimization/ (~496 statements).