docs: Fix data file naming in state-diagrams.md

Update data flow documentation to reflect actual file naming convention:
- Changed: wwwroot/data/{symbol}_gex.json
- To: wwwroot/data/{symbol}.json
- Added examples: spy.json, aapl.json

Verified against actual files in src/GexVisor.UI/wwwroot/data/

Related to comprehensive documentation audit (Session 24).

Author: iAmGiG

docs/state-diagrams.md

@@ -189,7 +189,7 @@ State flow from raw data files to visualization.
 ```
 
 **Data flow per symbol:**
-1. `wwwroot/data/{symbol}_gex.json` loaded
+1. `wwwroot/data/{symbol}.json` loaded (e.g., `spy.json`, `aapl.json`)
 2. Parsed to `GexTimeline` model
 3. Regime analysis computed
 4. Available via `GexStateService`