v0.5.0: the pages API of Hindsight 1.2.1

Tested against Hindsight 1.1.0, 1.2.0 and 1.2.1.

Added

• The pages API of Hindsight 1.2.1: getPageTree(), createPage(), createPageFolder(), getPage(), searchPages(), exportPages(), updatePageNode() and deletePageNode(), also on the facade. Requests to these endpoints are checked against the 1.2.1 OpenAPI document, and CI runs the page tree against a real 1.2.1 server (creating a page needs the server's LLM, so pages are covered by the unit tests). Hindsight::fake() does not simulate pages; stub them with respondTo().
• NotFoundException::isMissingBank(): whether a 404 says that the bank does not exist. Memory::isMissingBank() now calls it, and the MCP tools no longer use a class from the Laravel AI SDK integration.