docs: bring README/CONTRIBUTING/INSTALLATION up to v1.9.8

README:
- Journey section: add v1.9.5 (weather recovery), v1.9.6 (stability fixes via
  dual AI review), v1.9.7 (config validation), v1.9.8 (live config updates)
- Memory Evolution table: add v1.9.6 and v1.9.8 rows
- Project Structure: list all modular firmware files + tests/test_device.py
- Add Testing section explaining the 73-case hardware-in-the-loop suite
- Bump current version footer to v1.9.8

CONTRIBUTING:
- Flashing section: OTA preferred, FTDI fallback with exact esptool commands
- Add test suite invocation
- Add recovery section (triple power-cycle factory reset since v1.9.6)

INSTALLATION:
- New Factory Reset section explaining the 3x power-cycle trick
- New Verifying Installation section pointing to test_device.py

docs/INSTALLATION.md

@@ -499,6 +499,34 @@ To save memory, disable unused features:
 
 ---
 
+## Factory Reset (no tools needed)
+
+Since v1.9.6, three quick power cycles within 10 seconds trigger a factory reset:
+
+1. Power off the device
+2. Power on (briefly, < 10 sec)
+3. Power off, power on
+4. Power off, power on
+
+On the third boot the OLED shows `FACTORY RESET! WiFi: TJ56654-Setup Pass: 12345678`.
+Connect your phone to that AP and reconfigure WiFi at `http://192.168.4.1/config`.
+
+Use this if:
+
+- Forgot configured WiFi credentials
+- Device stuck in "No WiFi" loop after router change
+- Tests/fuzzing corrupted config
+
+## Verifying Installation
+
+Run the test suite against your device:
+
+```bash
+python3 tests/test_device.py 192.168.x.x
+```
+
+A healthy device passes all 73 tests, with heap drift under 1 KB across the run.
+
 ## Getting Help
 
 If you're still stuck: