Teach Joanna to maximize credit-card points by purchase category

## Goal

[private person] to help maximize household credit-card rewards without requiring the user to remember every card rule.

## Proposed capability

- Maintain a structured, reviewable catalog of cards, reward currencies, bonus categories, caps, activation requirements, redemption options, and expiration or devaluation considerations.
- Normalize merchant and purchase descriptions into discovery categories such as groceries, dining, travel, gas, transit, utilities, online retail, and recurring bills.
- Before a planned purchase, recommend the best eligible card and explain the expected points or miles outcome, relevant caps, and important caveats.
- When a transaction is ambiguous, ask a focused clarification instead of making a confident category assumption.
- Support redemption guidance by comparing transfer partners, statement credits, travel redemptions, and other available uses on a value-per-point basis.
- Keep the rules and recommendations date-aware so outdated offers or category terms are not presented as current.
- Provide a way to review why a recommendation was made and update the catalog when card terms change.

## Acceptance direction

A user should be able to ask which card to use for a planned purchase and receive a concise, explainable recommendation grounded in the current card/category catalog, with a safe fallback when the category or terms are uncertain.

This issue is a Joanna capability research and design track; it should not store card numbers, account credentials, or other sensitive financial data.

_Private person/location details were generalized for public tracking._

No files, tests, or entry points are named; treat this as a Joanna capability research and design track. Start by locating how Joanna capabilities are represented in the Home Assistant configuration, then define the card catalog, category handling, explainable recommendations, and uncertainty fallback. Done means a current, reviewable recommendation without storing card numbers or credentials.

Written by the indexing model from the issue text.