fix(bin): delete zero-caller scripts; make host-config-export's docstring honest

- bin/gstack-open-url (14 lines): announced in a CHANGELOG entry, wired into
  nothing, ever. bin/gstack-platform-detect (27 lines): zero callers, and its
  hand-rolled host list was already stale (SLATE_HOST.md cites it as a
  problem). Note: the deprecated gstack-brain-consumer/reader pair the audit
  flagged was already deleted upstream in v1.63 with a stay-deleted tripwire.
- scripts/task-emission-schema.ts (61 lines): a typed schema module nothing
  imported; the tasks-section comment now documents the JSONL fields inline.
- scripts/host-config-export.ts claimed to be the 'shell bridge for the bash
  setup script' — setup never calls it (its hand-rolled host lists drifting
  is a known follow-up). Docstring now states what it IS: a standalone,
  test-pinned query CLI not yet wired into setup. Its validateValue +
  CLI_REGEX/PATH_REGEX internals were dead (defined for a guarantee the
  header claimed but nothing enforced).
- KEPT deliberately: scripts/preflight-agent-sdk.ts — a documented manual
  diagnostic (CONTRIBUTING.md + USING_GBRAIN_WITH_GSTACK.md reference it).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/host-config-export.ts

@@ -1,6 +1,10 @@
 #!/usr/bin/env bun
 /**
- * Export host configs as shell-safe values for consumption by the bash setup script.
+ * Standalone query CLI for host configs (list / get / detect / validate).
+ *
+ * NOT yet wired into ./setup — setup still hand-rolls its host lists (a
+ * known drift source; driving setup from this CLI is queued follow-up work).
+ * Behavior is pinned by test/host-config.test.ts.
  *
  * Usage: bun run scripts/host-config-export.ts <command> [args]
  *
@@ -18,19 +22,11 @@ import { validateAllConfigs } from './host-config';
 import { RESOLVERS } from './resolvers';
 import { execSync } from 'child_process';
 
-const CLI_REGEX = /^[a-z][a-z0-9_-]*$/;
-const PATH_REGEX = /^[a-zA-Z0-9_.\/${}~-]+$/;
 
 function shellEscape(s: string): string {
   return "'" + s.replace(/'/g, "'\\''") + "'";
 }
 
-function validateValue(val: string, context: string): void {
-  if (!PATH_REGEX.test(val) && !CLI_REGEX.test(val)) {
-    throw new Error(`Unsafe value for ${context}: ${val}`);
-  }
-}
-
 const [command, ...args] = process.argv.slice(2);
 
 switch (command) {