Move MCP "runtime" logic to mcp crate.

[vorporeal]

Description

Moves the rmcp-heavy MCP server runtime out of the app crate and into crates/mcp so transport setup, preflight/authentication, server spawning, logging, and capability-query helpers live with the rest of the MCP application code.

Also moves templatable MCP OAuth handling into mcp; the app manager now only supplies app-specific state/UI callbacks for secure-storage persistence, pending auth state, URL opening, and success toasts. DateTimeExt moved to warp_core so shared code no longer depends on app server modules.

Testing

• cargo fmt
• cargo check -p mcp
• cargo check -p warp
• cargo nextest run -p mcp

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode
• Conversation: https://staging.warp.dev/conversation/bc883150-27d3-4f42-b99a-ae6be2a4226a

CHANGELOG-NONE

Co-Authored-By: Oz oz-agent@warp.dev

[vorporeal]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Move MCP "runtime" logic to mcp crate. #11378 👈 (View in Graphite)
• Extract cloud object persistence logic to other crates. #11179 : 1 other dependent PR (#11487 )
• Extract CloudObject client and models to separate crates. #11166
• Create cloud_objects crate. #11165
• Move cloud object models to separate crate. #11164
• Move GenericStringModel to warp_server_client. #11117
• Move GenericCloudObject to warp_server_client. #11115
• Move GenericServerObject to warp_server_client. #11114
• Move some types to the warp_server_client crate. #11113
• Delete unused new_from_server_update function. #11112
• master

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