Add firmware/ directory and update file scanning logic

- Add firmware/ directory to hold firmware files for techs cloning the repo
- Scan firmware/ (relative to script location) instead of CWD
- Add .fwc to supported firmware extensions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -23,6 +23,7 @@ No external dependencies — Python 3 standard library only. Compatible with Tru
 
 ```
 es24n_conf.py               ← Entry point and main menu (run this)
+firmware/                   ← Firmware files (.bin, .img, .fw, etc.) — scanned at update time
 modules/
     ui.py                   ← ANSI colours, display helpers, input prompts
     serial_port.py          ← SerialPort class (termios/fcntl/select, no pyserial)
@@ -53,7 +54,7 @@ Updates IOM firmware and/or Fabric Card firmware over the network:
 - Polls `/redfish/v1/TaskService/Tasks/` until completion
 - Restarts the IOM (and fabric card if applicable) after each update
 - The firmware file must be re-uploaded between the IOM and Fabric Card steps — it does not persist after the first update (firmware quirk, documented in `_update_fabric_fw()`)
-- Scans the current working directory for firmware files (`.bin`, `.img`, `.fw`, `.hex`, `.zip`, `.tar`, `.tgz`, `.gz`) and presents them as a numbered list before falling back to manual path entry
+- Scans the `firmware/` directory (next to `es24n_conf.py`) for firmware files (`.bin`, `.img`, `.fw`, `.fwc`, `.hex`, `.zip`, `.tar`, `.tgz`, `.gz`) and presents them as a numbered list before falling back to manual path entry
 
 ### 3 — System Check (`workflow_check.py`)
 Read-only diagnostic workflow — queries current network settings and firmware versions, makes no changes: