refactor: update commands, workflows, agents for gsd-tools integration

Commands (15): audit-milestone, complete-milestone, debug, execute-phase,
help, insert-phase, new-milestone, new-project, plan-milestone-gaps,
plan-phase, progress, quick, remove-phase, research-phase, verify-work

Workflows (22): execute-plan (69% reduction), verify-phase (55%), others
Agents (14): All updated for new workflow structure

Total token savings: ~22k chars (75.6% in affected sections)

Ported from: get-shit-done-v2@d1fb2d5, 7f79a9b

.planning/config.json.example

@@ -0,0 +1,14 @@
+{
+  "model_profile": "balanced",
+  "commit_docs": true,
+  "search_gitignored": false,
+  "branching_strategy": "none",
+  "phase_branch_template": "gsd/phase-{phase}-{slug}",
+  "milestone_branch_template": "gsd/{milestone}-{slug}",
+  "workflow": {
+    "research": true,
+    "plan_check": true,
+    "verifier": true
+  },
+  "parallelization": true
+}