refactor: update investment_prompts.json to use JSON format instead of pipes

- Updated EFFECTIVE_DT field: Replaced all pipe format examples (|date|) with JSON dictionary format
  - Changed examples from 'return |3-1  , , 03|' to 'return "3-1  , , 03"'
  - Updated final answer format from 'ENCLOSED in |pipes|' to JSON dict: {"EFFECTIVE_DT": "date"}
- Updated PROVIDER_NAME field: Replaced pipe-separated format with JSON list format
  - Changed from 'separated by |' to JSON list: ["Provider A", "Provider B"]
  - Updated to return JSON dict: {"PROVIDER_NAME": [...]} or {"PROVIDER_NAME": "single"}
- All pipe references removed from investment_prompts.json
- Updated PRD to document this change in Phase 2 checklist
- JSON file validated and syntax confirmed correct

docs/PRD_STANDARDIZE_LIST_FORMATS.md

@@ -2756,6 +2756,10 @@ def test_parsing_performance():
     - [x] All special case breakout `_INSTRUCTION()` functions (already JSON)
   - [x] Verified dynamic prompt functions remain clean (NO format instructions added)
   - [x] **All 35 prompt template functions now return `(prompt, parser)` tuples**
+- [x] Update `src/prompts/investment_prompts.json` ✅ **COMPLETE**
+  - [x] `EFFECTIVE_DT` field: Replaced pipe format examples and "ENCLOSED in |pipes|" instruction with JSON dictionary format
+  - [x] `PROVIDER_NAME` field: Replaced "separated by ' | '" instruction with JSON list format for multiple values
+  - [x] All pipe references removed from field prompts
 - [ ] Manual QA testing
   - [ ] Test each updated prompt with real LLM
   - [ ] Verify JSON format compliance