refactor: rename binary from quoteforge to qfs

- Rename cmd/server to cmd/qfs for shorter binary name
- Update all documentation references (README, CLAUDE.md, etc.)
- Update build commands to output bin/qfs
- Binary name now matches directory name

Usage:
  go run ./cmd/qfs              # Development
  go build -o bin/qfs ./cmd/qfs # Production

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -134,9 +134,9 @@ Go 1.22+ | Gin | GORM | MariaDB 11 | SQLite (glebarez/sqlite) | htmx + Tailwind
 
 ## Commands
 ```bash
-go run ./cmd/server          # Dev server
+go run ./cmd/qfs          # Dev server
 go run ./cmd/cron -job=X     # cleanup-pricelists | update-prices | update-popularity
-CGO_ENABLED=0 go build -ldflags="-s -w" -o bin/quoteforge ./cmd/server
+CGO_ENABLED=0 go build -ldflags="-s -w" -o bin/qfs ./cmd/qfs
 ```
 
 ## Code Style