docs: update documentation to match refactored codebase

- Delete obsolete plans/code-review.md (all suggestions implemented)
- Rewrite docs/API.md to reflect modular architecture, DashMap, corrected
  AppError variants, accurate function signatures and module locations
- Rewrite docs/ARCHITECTURE.md to reflect DashMap concurrency, remove
  completed future enhancements, fix AnalysisContext description
- Update docs/USER_GUIDE.md with global CLI path options (--my-cars,
  --cars-db, --times-dir, --tracks-db) and updated troubleshooting

docs/USER_GUIDE.md

@@ -47,6 +47,22 @@ Fetching https://api.topdrivesrecords.com/car/1002.json.
 
 ## Command Reference
 
+### Global Options
+
+All commands accept these optional flags to customize file paths:
+
+| Flag | Default | Description |
+|------|---------|-------------|
+| `--my-cars <PATH>` | `my_cars.json` | Path to user's car collection export |
+| `--cars-db <PATH>` | `cars_repo.json` | Path to car database file |
+| `--times-dir <DIR>` | `times` | Directory containing per-car timing JSON files |
+| `--tracks-db <PATH>` | `tracks_repo.json` | Path to tracks database file |
+
+**Example with custom paths:**
+```bash
+cargo run --bin records -- --cars-db /data/cars.json --times-dir /data/times best
+```
+
 ### Basic Analysis Commands
 
 #### Best Cars Analysis
@@ -407,12 +423,13 @@ The tool generates CSV files for external analysis. All files are sorted by car
 **Problem:** No arguments provided
 **Solution:** Use `best`, `trash`, `wishlist`, `all`, `details`, `track`, or `fetch`
 
-#### "Could not read my cars file"
-**Problem:** `my_cars.json` not found or not readable
+#### "Could not read my cars file" / "Missing data file"
+**Problem:** `my_cars.json` (or another data file) not found or not readable
 **Solution:**
 1. Export fresh data from Top Drives game
-2. Ensure file is named exactly `my_cars.json`
+2. Ensure file is named exactly `my_cars.json` (or use `--my-cars <PATH>` to specify a custom location)
 3. Check file permissions
+4. If `cars_repo.json` is missing, run `fetch` first (or use `--cars-db <PATH>`)
 
 #### "Failed to fetch the file"
 **Problem:** Network issues or API unavailable