feat(workflows): auto-copy learnings to global store at phase completion (#1828)

* feat(workflows): add auto-copy learnings to global store at phase completion

* fix(workflows): address review feedback for learnings auto-copy

- Replace shell-interpolated ${phase_dir} with agent context instruction
- Remove unquoted glob pattern in bash snippet
- Use gsd-tools learnings copy instead of manual file detection
- Document features.* dynamic namespace in config.cjs

* docs(config): add features.* namespace to CONFIGURATION.md schema

get-shit-done/bin/lib/config.cjs

@@ -43,6 +43,10 @@ function isValidConfigKey(keyPath) {
   if (VALID_CONFIG_KEYS.has(keyPath)) return true;
   // Allow agent_skills.<agent-type> with any agent type string
   if (/^agent_skills\.[a-zA-Z0-9_-]+$/.test(keyPath)) return true;
+  // Allow features.<feature_name> — dynamic namespace for feature flags.
+  // Intentionally open-ended so new flags (e.g., features.global_learnings) work
+  // without updating VALID_CONFIG_KEYS each time.
+  if (/^features\.[a-zA-Z0-9_]+$/.test(keyPath)) return true;
   return false;
 }