feat(#2182): scaffold community capability + EoS registry (tests + stubbed core)

Adds the discoverability-registry surface for issue #2182: JSON-sourced
capability/eos catalogs, a pure schema/vocab module (registry-schema.cjs)
with the ADR-857 loop points + ADR-1239 axes, thin validate/gen CLIs,
the registry-entry PR template, README spec, and CONTEXT.md glossary terms.

The three pure functions (isValidGsdRange/validateEntries/renderMarkdown)
are stubbed here so the comprehensive test suite fails first (red), per the
feature-implementation red-first directive; the next commit implements them.

Refs #2182

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/validate-registry.cjs

@@ -0,0 +1,117 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * scripts/validate-registry.cjs — CLI validator for the third-party
+ * discoverability catalogs (issue #2182):
+ *
+ *   - docs/registries/capabilities.json  ("GSD Community Capability Registry")
+ *   - docs/registries/eos.json           ("GSD EoS Registry", PR2 — optional
+ *     until that JSON file ships)
+ *
+ * Validates each source's JSON array against the closed schema in
+ * scripts/registry-schema.cjs (validateEntries). Human-readable errors go to
+ * stderr; `--json` additionally prints a structured verdict to stdout.
+ *
+ * Usage:
+ *   node scripts/validate-registry.cjs           # human-readable report
+ *   node scripts/validate-registry.cjs --json    # structured JSON verdict
+ *
+ * Exit codes:
+ *   0  every present source's entries are all valid
+ *   1  one or more entries failed validation (or a source's JSON is malformed)
+ */
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+const { ExitError, runMain } = require('./lib/cli-exit.cjs');
+const { validateEntries } = require('./registry-schema.cjs');
+
+// Resolved relative to process.cwd() (not __dirname) so the CLI validates
+// whichever project it is invoked from — this is what lets tests drive it as
+// a subprocess against isolated temp-fixture directories via `cwd`.
+const SOURCES = [
+  { file: 'capabilities.json', type: 'capability' },
+  { file: 'eos.json', type: 'eos' },
+];
+
+/**
+ * Load + validate a single registry JSON file.
+ *
+ * @param {string} jsonPath  absolute path to the registry JSON file
+ * @param {'capability'|'eos'} type
+ * @returns {{ok: boolean, errors: Array<{index: number, id?: string, field: string, reason: string}>}}
+ */
+function validateFile(jsonPath, type) {
+  let raw;
+  try {
+    raw = fs.readFileSync(jsonPath, 'utf8');
+  } catch (err) {
+    return {
+      ok: false,
+      errors: [{ index: -1, field: '<file>', reason: `could not read ${jsonPath}: ${err.message}` }],
+    };
+  }
+
+  let entries;
+  try {
+    entries = JSON.parse(raw);
+  } catch (err) {
+    return {
+      ok: false,
+      errors: [{ index: -1, field: '<file>', reason: `JSON parse error in ${jsonPath}: ${err.message}` }],
+    };
+  }
+
+  if (!Array.isArray(entries)) {
+    return {
+      ok: false,
+      errors: [{ index: -1, field: '<file>', reason: `${jsonPath} must be a JSON array of entries` }],
+    };
+  }
+
+  return validateEntries(entries, { type });
+}
+
+function main() {
+  const jsonMode = process.argv.includes('--json');
+  const registriesDir = path.join(process.cwd(), 'docs', 'registries');
+
+  const results = [];
+  let anyFailed = false;
+
+  for (const { file, type } of SOURCES) {
+    const jsonPath = path.join(registriesDir, file);
+    // eos.json is optional until PR2 ships it — skip silently when absent.
+    if (type === 'eos' && !fs.existsSync(jsonPath)) continue;
+
+    const verdict = validateFile(jsonPath, type);
+    results.push({ file, type, ok: verdict.ok, errors: verdict.errors });
+    if (!verdict.ok) anyFailed = true;
+  }
+
+  if (jsonMode) {
+    process.stdout.write(JSON.stringify({ ok: !anyFailed, results }, null, 2) + '\n');
+  } else if (anyFailed) {
+    process.stderr.write('\nERROR validate-registry: one or more entries failed validation\n');
+    for (const result of results) {
+      if (result.ok) continue;
+      process.stderr.write(`\n${result.file}:\n`);
+      for (const e of result.errors) {
+        const idPart = e.id ? ` (id: ${e.id})` : '';
+        process.stderr.write(`  entry[${e.index}]${idPart} field "${e.field}": ${e.reason}\n`);
+      }
+    }
+    process.stderr.write('\n');
+  } else {
+    process.stdout.write('ok validate-registry: all entries valid\n');
+  }
+
+  if (anyFailed) throw new ExitError(1, 'registry validation failed');
+  return 0;
+}
+
+if (require.main === module) runMain(main);
+
+module.exports = { main, validateFile, SOURCES };