fix: Add CLI flag reference to JSDoc, improve initComptime warning

- Add "Equivalent to the CLI --feature flag" to bun.d.ts JSDoc
- Improve initComptime doc comment warning about undefined behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/bun-types/bun.d.ts

@@ -1897,6 +1897,8 @@ declare module "bun" {
      * When `feature("FLAG_NAME")` is called, it returns `true` if FLAG_NAME is in this array,
      * or `false` otherwise. This enables static dead-code elimination at bundle time.
      *
+     * Equivalent to the CLI `--feature` flag.
+     *
      * @example
      * ```ts
      * await Bun.build({

src/bun.zig

@@ -1623,8 +1623,8 @@ pub const StringSet = struct {
     }
 
     /// Initialize an empty StringSet at comptime (for use as a static constant).
-    /// WARNING: The resulting set has an undefined allocator and must not be mutated.
-    /// Do not call insert(), clone(), or any method that allocates on a comptime-initialized set.
+    /// WARNING: The resulting set must not be mutated. Any attempt to call insert(),
+    /// clone(), or other allocating methods will result in undefined behavior.
     pub fn initComptime() StringSet {
         return StringSet{
             .map = Map.initContext(undefined, .{}),