Add tool annotations and PR close/reopen support (#174)

Add MCP `ToolAnnotation` metadata (Title, ReadOnlyHint, DestructiveHint)
to all registered tools so MCP hosts (VS Code, Claude, Cursor) get
accurate per-tool hints. A shared `pkg/annotation` package exposes
`ReadOnly`, `Write`, and `Destructive` helpers for consistency.

Add `close` and `reopen` methods to `pull_request_write` so PR state
can be toggled without going through the generic `update` path.

Co-Authored-By: silverwind <me@silverwind.io>
Co-Authored-By: Claude (Opus 4.7) <noreply@anthropic.com>

pkg/annotation/annotation.go

@@ -0,0 +1,32 @@
+// Package annotation provides shared MCP tool annotation helpers.
+package annotation
+
+import "github.com/mark3labs/mcp-go/mcp"
+
+// ReadOnly returns a ToolAnnotation for read-only tools.
+func ReadOnly(title string) mcp.ToolAnnotation {
+	t := true
+	return mcp.ToolAnnotation{
+		Title:        title,
+		ReadOnlyHint: &t,
+	}
+}
+
+// Write returns a ToolAnnotation for write tools.
+func Write(title string) mcp.ToolAnnotation {
+	f := false
+	return mcp.ToolAnnotation{
+		Title:        title,
+		ReadOnlyHint: &f,
+	}
+}
+
+// Destructive returns a ToolAnnotation for destructive write tools.
+func Destructive(title string) mcp.ToolAnnotation {
+	f, t := false, true
+	return mcp.ToolAnnotation{
+		Title:           title,
+		ReadOnlyHint:    &f,
+		DestructiveHint: &t,
+	}
+}