refactor: apply code-review findings to github-native coordination

scripts/github-coordination.js:
- parseArgs: replace 13-entry if/else chain with BOOL_FLAGS/VALUE_FLAGS
  lookup maps; shrinks from 119 to ~45 lines
- Extract dispatchCommand(options, ctx) and formatOutput(payload, options)
  from main(); main() shrinks to ~20 lines

scripts/lib/github-coordination.js:
- Split 1041-line monolith into 6 focused sub-modules under
  scripts/lib/github-coordination/ (policy, parsing, gh-api, state,
  actions, store); index becomes a thin re-export (~55 lines)
- Document ECC_GH_SHIM trust boundary in runGh() (gh-api.js)
- Document applyClaim() read→check→write race condition (actions.js)

tests/lib/github-coordination.test.js:
- Refactor runTests() to data-driven DESCRIPTORS array + runGroup()
  helper; runTests() shrinks to ~10 lines
- Add 5 new edge-case tests: normalizeRepo('') and normalizeRepo('   ')
  throw, desiredLabelsForState for blocked/ready statuses, and
  buildIssueStateFromAction for validate action (15 → 20 tests)

tests/scripts/github-coordination.test.js:
- Replace console.log in test runner with process.stdout.write

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/lib/github-coordination/policy.js

@@ -0,0 +1,107 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+
+const DEFAULT_CONFIG_FILE = 'github-native-coordination.json';
+const DEFAULT_CONFIG_PATH = path.join(__dirname, '..', '..', '..', 'config', DEFAULT_CONFIG_FILE);
+const DEFAULT_SECTION_MARKER = 'ecc-coordination';
+const DEFAULT_SCHEMA_VERSION = 'ecc.github.coordination.v1';
+const DEFAULT_LABELS = Object.freeze({
+  epic: 'epic',
+  available: 'coordination:available',
+  claimed: 'coordination:claimed',
+  ready: 'coordination:ready',
+  blocked: 'coordination:blocked',
+  validated: 'coordination:validated',
+  reviewRequested: 'coordination:review-requested',
+  reviewApproved: 'coordination:review-approved',
+  reviewChangesRequested: 'coordination:review-changes-requested',
+  published: 'coordination:published',
+  synced: 'coordination:synced',
+});
+const DEFAULT_POLICY = Object.freeze({
+  schemaVersion: DEFAULT_SCHEMA_VERSION,
+  sectionMarker: DEFAULT_SECTION_MARKER,
+  labels: DEFAULT_LABELS,
+  review: {
+    required: true,
+    defaultMode: 'required',
+  },
+  validation: {
+    required: true,
+  },
+  branchModel: {
+    epicOnly: true,
+    taskBranches: false,
+  },
+  project: {
+    enabled: false,
+    fieldNames: {
+      status: 'Status',
+      owner: 'Owner',
+      branch: 'Branch',
+      validation: 'Validation',
+      review: 'Review',
+    },
+  },
+});
+
+function loadPolicy(rootDir = process.cwd(), configPath = null) {
+  const resolvedPath = configPath
+    ? path.resolve(configPath)
+    : path.join(rootDir, 'config', DEFAULT_CONFIG_FILE);
+
+  if (!fs.existsSync(resolvedPath)) {
+    return {
+      ...DEFAULT_POLICY,
+      sourcePath: null,
+    };
+  }
+
+  let parsed;
+  try {
+    parsed = JSON.parse(fs.readFileSync(resolvedPath, 'utf8'));
+  } catch (error) {
+    throw new Error(`Failed to load policy from ${resolvedPath}: ${error.message}`);
+  }
+  return {
+    ...DEFAULT_POLICY,
+    ...parsed,
+    labels: {
+      ...DEFAULT_LABELS,
+      ...(parsed.labels || {}),
+    },
+    review: {
+      ...DEFAULT_POLICY.review,
+      ...(parsed.review || {}),
+    },
+    validation: {
+      ...DEFAULT_POLICY.validation,
+      ...(parsed.validation || {}),
+    },
+    branchModel: {
+      ...DEFAULT_POLICY.branchModel,
+      ...(parsed.branchModel || {}),
+    },
+    project: {
+      ...DEFAULT_POLICY.project,
+      ...(parsed.project || {}),
+      fieldNames: {
+        ...DEFAULT_POLICY.project.fieldNames,
+        ...((parsed.project || {}).fieldNames || {}),
+      },
+    },
+    sourcePath: resolvedPath,
+  };
+}
+
+module.exports = {
+  DEFAULT_CONFIG_FILE,
+  DEFAULT_CONFIG_PATH,
+  DEFAULT_LABELS,
+  DEFAULT_POLICY,
+  DEFAULT_SCHEMA_VERSION,
+  DEFAULT_SECTION_MARKER,
+  loadPolicy,
+};