03 implement

Implement a feature from a prd.

Guardrails

• Follow the repo's AGENTS.md instructions (if present) for any files you touch.
• Keep changes simple and handoff-friendly: assume a junior dev (or another AI) will maintain this later.
• Do not change product scope while executing:
  • If the prd is missing details or ambiguous, stop and use 02-plan to refine the prd first.
  • If the feature is missing from tasks/todo.md, stop and use 01-new first.
  • If you discover out-of-scope requirements or bugs during execution, do not expand scope—create a new backlog item via 01-new instead.
• Do not edit tasks/todo.md except updating this feature's status indicator from — to 🔨 when implementation is complete.
• Do not reset any prd status checkboxes when updating an existing prd.