Add MCP App form deferral opt-out

[connor4312]

MCP Apps in the GitHub MCP Server are useful, but having issue and pull request tools open a form instead of performing the requested operation can be disruptive, especially in autopilot workflows where autonomous task completion is expected.

This adds the user-controllable mcp_apps_disable_form_deferral feature flag. When enabled alongside remote_mcp_ui_apps, form-backed write tools execute directly while MCP App result views and UI metadata remain enabled. HTTP clients can opt in per request through X-MCP-Features.

Testing

• script/lint
• script/test
• Built and exercised the stdio MCP server through initialize, tools/list, and tools/call exchanges
• Verified the baseline configuration defers issue_write to its interactive form
• Verified the opt-out executes directly and preserves issue_write MCP App UI metadata

[Copilot]

Pull request overview

Adds a user-controlled feature flag to bypass MCP App form deferral while preserving UI metadata and result views.

Changes:

• Adds and documents mcp_apps_disable_form_deferral.
• Applies the opt-out across form-backed issue and pull-request tools.
• Tests feature resolution, HTTP headers, insiders mode, and deferral behavior.

Show a summary per file

File	Description
pkg/http/server_test.go	Tests HTTP-header and insiders behavior.
pkg/github/ui_capability.go	Adds the form-deferral opt-out check.
pkg/github/ui_capability_test.go	Tests deferral flag combinations.
pkg/github/feature_flags.go	Defines and allows the new flag.
pkg/github/feature_flags_test.go	Tests feature resolution behavior.
docs/server-configuration.md	Documents remote and local configuration.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0
• Review effort level: Medium