chore: remove obsolete planning files for Nuxt 4 migration

- Deleted several planning documents including config.json, PROJECT.md, REQUIREMENTS.md, ROADMAP.md, STATE.md, and various phase plans.
- These files were no longer relevant to the current project structure and development practices, streamlining the codebase.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.planning/config.json

@@ -1,41 +0,0 @@
-{
-  "model_profile": "balanced",
-  "commit_docs": true,
-  "parallelization": true,
-  "search_gitignored": false,
-  "brave_search": false,
-  "firecrawl": false,
-  "exa_search": false,
-  "git": {
-    "branching_strategy": "none",
-    "phase_branch_template": "gsd/phase-{phase}-{slug}",
-    "milestone_branch_template": "gsd/{milestone}-{slug}",
-    "quick_branch_template": null
-  },
-  "workflow": {
-    "research": true,
-    "plan_check": true,
-    "verifier": true,
-    "nyquist_validation": false,
-    "auto_advance": true,
-    "node_repair": true,
-    "node_repair_budget": 2,
-    "ui_phase": true,
-    "ui_safety_gate": true,
-    "text_mode": false,
-    "research_before_questions": false,
-    "discuss_mode": "discuss",
-    "skip_discuss": false,
-    "code_review": true,
-    "code_review_depth": "standard",
-    "_auto_chain_active": false
-  },
-  "hooks": {
-    "context_warnings": true
-  },
-  "project_code": null,
-  "phase_naming": "sequential",
-  "agent_skills": {},
-  "mode": "yolo",
-  "granularity": "coarse"
-}