feat: replace server instructions with skill resources

Replace the server instructions system with MCP skill resources that
follow the skill:// URI convention for discovery by MCP clients.

Each skill resource covers a domain of tools and provides YAML
frontmatter (name, description, allowed-tools) plus markdown guidance.

All tools remain available by default (all tools mode). Skills provide
contextual guidance that clients can discover via resources/list.

16 skills covering all toolsets: context, repos, issues, pull-requests,
code-security, actions, discussions, projects, notifications, gists,
users-orgs, security-advisories, labels, git, stargazers, copilot.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SamMorrowDrums

internal/ghmcp/server.go

@@ -143,7 +143,6 @@ func NewStdioMCPServer(ctx context.Context, cfg github.MCPServerConfig) (*mcp.Se
 		WithToolsets(github.ResolvedEnabledToolsets(cfg.DynamicToolsets, cfg.EnabledToolsets, cfg.EnabledTools)).
 		WithTools(github.CleanTools(cfg.EnabledTools)).
 		WithExcludeTools(cfg.ExcludeTools).
-		WithServerInstructions().
 		WithFeatureChecker(featureChecker)
 
 	// Apply token scope filtering if scopes are known (for PAT filtering)

pkg/github/server.go

@@ -81,7 +81,6 @@ type MCPServerOption func(*mcp.ServerOptions)
 func NewMCPServer(ctx context.Context, cfg *MCPServerConfig, deps ToolDependencies, inv *inventory.Inventory, middleware ...mcp.Middleware) (*mcp.Server, error) {
 	// Create the MCP server
 	serverOpts := &mcp.ServerOptions{
-		Instructions:      inv.Instructions(),
 		Logger:            cfg.Logger,
 		CompletionHandler: CompletionsHandler(deps.GetClient),
 	}
@@ -125,6 +124,9 @@ func NewMCPServer(ctx context.Context, cfg *MCPServerConfig, deps ToolDependenci
 		registerDynamicTools(ghServer, inv, deps, cfg.Translator)
 	}
 
+	// Register skill resources for MCP clients that support skills-based discovery
+	RegisterSkillResources(ghServer)
+
 	return ghServer, nil
 }