fix: populate custom targeting keys when editing products

[bokelley]

Summary

Fixed issue where custom targeting keys weren't showing as pre-selected when editing a product. The keys were saved correctly but the edit form wasn't displaying them.

Problem

When you:

1. Create a product with custom targeting keys (e.g., sport=basketball)
2. Save the product
3. Edit the product again

The custom targeting dropdown was empty instead of showing the previously selected keys.

Root Cause

The edit_product GET handler wasn't passing targeting_template to the template. The custom targeting keys were stored in implementation_config.custom_targeting_keys, but the form expects them in targeting_template.key_value_pairs.

Fix

Added logic to populate targeting_template from implementation_config when loading the edit form:

1. Parse both targeting_template and implementation_config from product
2. If targeting_template.key_value_pairs is empty but implementation_config.custom_targeting_keys exists, copy the keys
3. Pass the populated targeting_template to the template

This provides backwards compatibility for products that have keys stored only in implementation_config.

Test Coverage

• ✅ Unit tests: 861 passed
• ✅ Integration tests: 32 passed
• ✅ Integration V2 tests: 28 passed
• ✅ All pre-commit hooks passed

Result

• ✅ Custom targeting keys now show as pre-selected when editing products
• ✅ Form correctly displays existing key/value pairs
• ✅ Backwards compatible with existing products

🤖 Generated with Claude Code