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>

bin/gstack-open-url

@@ -1,14 +0,0 @@
-#!/usr/bin/env bash
-# gstack-open-url — cross-platform URL opener
-#
-# Usage: gstack-open-url <url>
-set -euo pipefail
-
-URL="${1:?Usage: gstack-open-url <url>}"
-
-case "$(uname -s)" in
-  Darwin)  open "$URL" ;;
-  Linux)   xdg-open "$URL" 2>/dev/null || echo "$URL" ;;
-  MINGW*|MSYS*|CYGWIN*) start "$URL" ;;
-  *)       echo "$URL" ;;
-esac

bin/gstack-platform-detect

@@ -1,27 +0,0 @@
-#!/usr/bin/env bash
-set -euo pipefail
-
-# gstack-platform-detect: show which AI coding agents are installed and gstack status
-# Config-driven: reads host definitions from hosts/*.ts via host-config-export.ts
-
-SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-GSTACK_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
-
-printf "%-16s %-10s %-40s %s\n" "Agent" "Version" "Skill Path" "gstack"
-printf "%-16s %-10s %-40s %s\n" "-----" "-------" "----------" "------"
-
-for host in $(bun run "$GSTACK_DIR/scripts/host-config-export.ts" list 2>/dev/null); do
-  cmd=$(bun run "$GSTACK_DIR/scripts/host-config-export.ts" get "$host" cliCommand 2>/dev/null)
-  root=$(bun run "$GSTACK_DIR/scripts/host-config-export.ts" get "$host" globalRoot 2>/dev/null)
-  spath="$HOME/$root"
-
-  if command -v "$cmd" >/dev/null 2>&1; then
-    ver=$("$cmd" --version 2>/dev/null | head -1 || echo "unknown")
-    if [ -d "$spath" ] || [ -L "$spath" ]; then
-      status="INSTALLED"
-    else
-      status="NOT INSTALLED"
-    fi
-    printf "%-16s %-10s %-40s %s\n" "$host" "$ver" "$spath" "$status"
-  fi
-done