Auto-activate editor Copilot skills by project type

[nighca]

Background

Issue #2808 establishes the project-type-agnostic Copilot skill mechanism, but the initial design intentionally only supports tool-based model-driven activation.

For editor pages, we may want a stronger default: when the active project type is already known, the editor can proactively activate the corresponding class-framework skill so the model does not need to discover and load it on its own.

What This Issue Is About

Add support for the editor page to automatically activate a specific Copilot skill based on the current project type or class framework.

The goal is to make framework-specific guidance available earlier and more reliably for editing tasks, while keeping the generic skill mechanism from #2808 intact.

Scope

• Define when editor-owned automatic activation should happen, for example when entering the editor or when the active project changes.
• Resolve the target skill from project type or class framework information already available to the editor.
• Reuse the existing skill-loading mechanism instead of introducing a separate skill format.
• Ensure repeated activation is deduplicated so navigation or reactive updates do not keep injecting the same skill.
• Define how auto-activated skills interact with manually model-triggered load_skill calls.

Out of Scope

• Automatic activation outside editor pages
• User-explicit activation UX
• New skill authoring or packaging format

Done When

• Opening an editor for a supported project type automatically makes the expected framework-specific skill available to Copilot.
• Switching editors or project types updates the activated skill set without leaving stale framework knowledge behind.
• Duplicate activations are safely deduplicated.
• The behavior is covered by tests.