Trace a card's blocking history

# A card's blocking history

## Difference from the blocking field on get_card / list_cards

`get_card` and `list_cards` expose a `blockingReason` field that only shows the **current** state. For a card blocked and unblocked several times, or blocked for several reasons at once, that field isn't enough — `get_card_blocking_history` returns the full history, including reasons already cleared.

## Call

```json
{
  "tool": "get_card_blocking_history",
  "params": {
    "companyId": "<companyId>",
    "cardId": "<cardId>"
  }
}
```

## Reading the result

- Result is ordered most-recent-first.
- `endedAt: null` means this blocking reason is **still active** — several rows can have `endedAt: null` at the same time, since a card can be blocked for multiple reasons simultaneously.
- `blockerId` is only populated (with the raw user id, no name resolved) when `initiator="user"` — never invent a name from this field.
- **An empty array (`{"data":[]}`) is a normal result** for a card that's never been blocked — verified across several active cards on this account, none had any history, which is the expected case for incident-free cards.

## Observed example

```json
{"data":[]}
```

On an active card with no incidents — read as "never blocked", not as missing data or an error.

## Example user prompts

- "Why was [employee]'s card blocked three times this quarter?"
- "Is this card currently blocked for more than one reason at once?"
- "List the full blocking history for card [XXXX]"