Support MCP resources with automatic context inclusion for remote connectors

### Problem Statement

Claude.ai supports custom remote MCP connectors on Pro (including mobile), but currently only implements the tools primitive. This means any context retrieval from an MCP server requires the model to explicitly make a tool call. Memory servers like Hindsight (Vectorize.io) support automatic per-prompt recall via MCP, and other platforms (Grok Build, Microsoft Agent Framework) already implement this. Claude.ai cannot.

### Proposed Solution

Implement the automatic context inclusion pattern for MCP resources that the protocol already defines. This would allow remote MCP servers to provide resources that are loaded into the model's context per-prompt without requiring explicit tool invocation — similar to how userMemories are injected today.

### Alternatives Considered

Using MCP tools with "always available" enabled and custom instructions telling the model to query the memory server on every message. This is unreliable since it depends on the model choosing to comply, and lacks the guaranteed per-prompt behavior that resource-based injection provides. Related: anthropics/claude-code#7252

### Area

MCP Connector (adding/managing servers)

### Priority

Critical - Blocking my MCP server development

### Additional Context

The MCP spec already defines this behavior. The infrastructure is in place. Other platforms implement it. For what it's worth, Claude would probably appreciate this one too.