Mark MCP tools as readonly for M365 federated connector support.

## Title
MCP tools missing `annotations` (readOnlyHint/destructiveHint) required by MCP spec and consumers like M365 Copilot Federated Connectors

## Summary
DAB's built-in MCP DML tools (`describe_entities`, `read_records`, `aggregate_records`, and presumably `create_record`/`update_record`/`delete_record`) do not emit an `annotations` object in their `tools/list` response. This blocks integration with MCP consumers that require tool annotations for safety validation — specifically, Microsoft 365 Copilot's federated connector, which rejects or silently drops tools lacking `readOnlyHint`.

## Current behavior
`tools/list` response for built-in tools has no `annotations` field, e.g.:

```json
{
"name": "read_records",
"description": "...",
"inputSchema": { ... }
}
```
## Expected behavior

Each tool should include an annotations object per the MCP spec, e.g.:

```json
{
"name": "read_records",
"description": "...",
"inputSchema": { ... },
"annotations": {
"readOnlyHint": true
}
}
```
At minimum, describe_entities, read_records, and aggregate_records should be marked readOnlyHint: true. Any write tools (create_record, update_record, delete_record) should be marked readOnlyHint: false and destructiveHint set appropriately (true for delete/update, false for create).

## Impact

Without this, DAB's MCP server cannot be registered as a custom connector in Microsoft 365 Copilot (and likely other MCP consumers enforcing the same validation), since these platforms require explicit read-only annotations before allowing a tool to be surfaced/executed.

## Environment
DAB version: 2.x (MCP support)
Consumer: Microsoft 365 Copilot federated connector (custom MCP connector)

Commencez par la réponse tools/list du serveur MCP et localisez les définitions intégrées des outils DML pour describe_entities, read_records, aggregate_records, create_record, update_record et delete_record. Comparez leur sortie aux exigences d’annotation de MCP, puis vérifiez que les outils en lecture seule et les outils d’écriture exposent les valeurs attendues de readOnlyHint et destructiveHint.

Rédigé par le modèle d'indexation à partir du texte de l'issue.