feat(auto-advance): chain phase execution across full milestone

Wire execute-phase to invoke transition.md inline when --auto flag or
workflow.auto_advance config is set, propagate --auto through transition
to next phase invocations, add config-get command to gsd-tools, and fix
broken "config get" calls to use hyphenated "config-get" subcommand.

Closes #344

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

get-shit-done/bin/gsd-tools.cjs

@@ -692,6 +692,42 @@ function cmdConfigSet(cwd, keyPath, value, raw) {
   }
 }
 
+function cmdConfigGet(cwd, keyPath, raw) {
+  const configPath = path.join(cwd, '.planning', 'config.json');
+
+  if (!keyPath) {
+    error('Usage: config-get <key.path>');
+  }
+
+  let config = {};
+  try {
+    if (fs.existsSync(configPath)) {
+      config = JSON.parse(fs.readFileSync(configPath, 'utf-8'));
+    } else {
+      error('No config.json found at ' + configPath);
+    }
+  } catch (err) {
+    if (err.message.startsWith('No config.json')) throw err;
+    error('Failed to read config.json: ' + err.message);
+  }
+
+  // Traverse dot-notation path (e.g., "workflow.auto_advance")
+  const keys = keyPath.split('.');
+  let current = config;
+  for (const key of keys) {
+    if (current === undefined || current === null || typeof current !== 'object') {
+      error(`Key not found: ${keyPath}`);
+    }
+    current = current[key];
+  }
+
+  if (current === undefined) {
+    error(`Key not found: ${keyPath}`);
+  }
+
+  output(current, raw, String(current));
+}
+
 function cmdHistoryDigest(cwd, raw) {
   const phasesDir = path.join(cwd, '.planning', 'phases');
   const digest = { phases: {}, decisions: [], tech_stack: new Set() };
@@ -4999,6 +5035,11 @@ async function main() {
       break;
     }
 
+    case 'config-get': {
+      cmdConfigGet(cwd, args[1], raw);
+      break;
+    }
+
     case 'history-digest': {
       cmdHistoryDigest(cwd, raw);
       break;