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/store.js

@@ -0,0 +1,65 @@
+'use strict';
+
+const os = require('os');
+
+const { createStateStore } = require('../state-store');
+const { DEFAULT_SCHEMA_VERSION, DEFAULT_POLICY } = require('./policy');
+const { normalizeLabels } = require('./gh-api');
+const { slugifySegment, mapStateToWorkItemStatus, summarizeProjectProjection } = require('./state');
+
+function epicWorkItemId(repo, issueNumber) {
+  return `github-${slugifySegment(repo)}-epic-${issueNumber}`;
+}
+
+function upsertCoordinationWorkItem(store, repo, issue, state, action, options = {}) {
+  if (!store) {
+    return null;
+  }
+
+  const now = new Date().toISOString();
+  const metadata = {
+    schemaVersion: state.schemaVersion || DEFAULT_SCHEMA_VERSION,
+    repo,
+    issueNumber: issue.number,
+    issueUrl: issue.url || null,
+    issueTitle: issue.title || null,
+    labels: normalizeLabels(issue.labels),
+    coordination: state,
+    projectProjection: summarizeProjectProjection(state, options.policy || DEFAULT_POLICY),
+    action,
+    actionAt: now,
+    syncedBy: 'ecc-github-coordination',
+  };
+
+  return store.upsertWorkItem({
+    id: epicWorkItemId(repo, issue.number),
+    source: 'github-epic',
+    sourceId: String(issue.number),
+    title: `Epic #${issue.number}: ${issue.title}`,
+    status: mapStateToWorkItemStatus(state.status),
+    priority: state.status === 'blocked' ? 'high' : 'normal',
+    url: issue.url || null,
+    owner: state.owner || (issue.author && issue.author.login) || null,
+    repoRoot: options.repoRoot || process.cwd(),
+    sessionId: options.sessionId || null,
+    metadata,
+    updatedAt: now,
+  });
+}
+
+async function openStore(options = {}) {
+  if (options.dbPath === false) {
+    return null;
+  }
+
+  return createStateStore({
+    dbPath: options.dbPath,
+    homeDir: options.homeDir || process.env.HOME || os.homedir(),
+  });
+}
+
+module.exports = {
+  epicWorkItemId,
+  openStore,
+  upsertCoordinationWorkItem,
+};