fix(mcp): follow nextCursor in prompts/list, resources/list and resources/templates/list #855

Problem

#825 (fixing #301) made Raven follow nextCursor for tools/list. The other three list operations the MCP spec makes paginated are still fetched as a single page:

Each site calls session.list_*() once and renders the items without looking at nextCursor. The Python SDK does not walk pages for the caller: in the pinned mcp 1.30.0, every ClientSession.list_* method sends exactly one request.

When a server paginates any of these lists, the model sees only the first page, and nothing tells it the list is incomplete. This is the same silent truncation as #301, on the remaining three verbs.

Evidence

• MCP spec, Pagination (unchanged from 2025-06-18 through 2026-07-28): "The following MCP operations support pagination: resources/list, resources/templates/list, prompts/list, tools/list." https://modelcontextprotocol.io/specification/2026-07-28/server/utilities/pagination
• The official TypeScript SDK client walks all four by default: listTools(), listPrompts(), listResources() and listResourceTemplates() follow nextCursor and return one aggregated list. https://github.com/modelcontextprotocol/typescript-sdk/blob/main/docs/clients/calling.md
• Python SDK, mcp/client/session.py: list_resources, list_resource_templates and list_prompts each build one request and return its result; there is no loop.

Impact

Lower than #301:

• read_mcp_resource (by URI) and get_mcp_prompt (by name) still work for an item the model already knows; only discovery through the three list tools is truncated.
• No user report yet, and we have not found a public server that paginates these lists today.

The gap is still deterministic: any server that pages one of these lists triggers it, and resource lists (files, documents, table rows) are where large counts are most plausible.

Proposed fix

• One shared helper in raven/mcp/ that walks a list verb page by page with params=PaginatedRequestParams(cursor=...) and stops on an empty or repeated cursor (the stop rule fix(mcp): page through tools/list nextCursor #825 introduced).
• Use it at the three call sites above, and move the tools/list loop from fix(mcp): page through tools/list nextCursor #825 onto it, so all four verbs share one implementation.
• Keep each list tool's existing 30s timeout, now around the whole walk, so a server that never stops paging fails visibly instead of stalling the turn.

Acceptance criteria

• Single-page servers behave exactly as before.
• Multi-page prompt, resource and resource-template lists return every item.
• A repeated cursor ends the walk.
• New tests in tests/test_mcp_prompts.py and tests/test_mcp_resources.py fail on current main and pass with the fix.
• make lint-types stays clean (no deprecated cursor= overload).

Related: #301, #825