v1.1: generic Linux monitoring with optional FRITZ!Box diagnostics

[LucaXTech]

Summary

This PR evolves LineWatch from a Raspberry-Pi/FRITZ!Box-specific monitor into a generic Linux Internet connection black box while preserving FRITZ!Box as the first enhanced router integration.

Generic Linux mode

• runs without router credentials
• auto-detects the IPv4 default gateway and interface
• monitors link state, gateway reachability, Internet ICMP, DNS, HTTP, public IP, outages and downtime
• avoids false outages when a gateway or upstream target intentionally drops ICMP
• keeps ISP report and CSV export useful without router-specific telemetry

FRITZ!Box enhanced mode

When TR-064 credentials are configured, LineWatch keeps the existing deep diagnostics:

• router model / FRITZ!OS
• router uptime and reboot detection
• WAN uptime / state
• WAN or PPPoE session-reset detection
• router event logs around incidents when available

User experience

• installer now offers generic or FRITZ-enhanced setup
• Raspberry Pi is a recommended always-on target rather than a hard requirement
• dashboard adapts automatically to the available telemetry
• README is repositioned around the connection-black-box use case

Open-source project hygiene

• MIT License, copyright Luca Serioli
• explicit creator/maintainer attribution
• contribution and security guidance
• compatibility, bug and feature-request templates
• Linux validation checklist
• expanded CI with unit tests and shell syntax checks

Validation

CI

• GitHub Actions passes on Python 3.11 and 3.13
• classifier and route-detection unit tests pass
• shell scripts pass syntax checks
• outage timestamp/duration regression coverage added after physical testing

WSL2 smoke test — passed

Validated on Windows WSL2 with Ubuntu 26.04 LTS x86_64 and Python 3.14.4:

• 14/14 unit tests passed at the time of the WSL validation
• generic setup and route/interface autodetection passed
• gateway-ICMP fallback behaved correctly: the WSL virtual gateway did not answer ICMP while Internet/DNS/HTTP remained healthy, and no false outage was raised
• dashboard, API, SQLite history and public-IP observation worked
• full install.sh path worked
• linewatch.service and linewatch-dashboard.service ran successfully under systemd/Waitress
• services returned automatically after wsl --shutdown and a fresh WSL start
• FRITZ!Box enhanced mode was re-checked over the real LAN using an explicitly configured router address; TR-064 returned model, FRITZ!OS, router uptime, WAN status/uptime, PPPoE metadata and reconnect timing with no regression observed

Physical Raspberry Pi validation — passed

Validated on an Ethernet-connected Raspberry Pi running Debian 13 (trixie) arm64:

• shell-script executable permissions verified from a fresh branch checkout
• generic mode auto-detected the physical eth0 interface and real IPv4 default gateway
• gateway ICMP capability detection passed
• FRITZ!Box enhanced mode passed against a real FRITZ!Box 5530 Fiber using TR-064, including model, FRITZ!OS, router uptime, WAN state/uptime and PPPoE telemetry
• physical Ethernet unplug correctly produced NETWORK_LINK_DOWN, rather than a generic gateway/Internet outage
• monitor survived loss of SSH/network connectivity and detected recovery after reconnect
• post-recovery carrier, gateway, Internet, DNS and HTTP checks all returned healthy
• physical testing exposed an outage-duration timing inconsistency; the monitor now uses a consistent cycle-time reference for event timestamps and monotonic duration measurement
• regression suite increased to 15/15 passing tests
• a second physical unplug after the fix produced a 20.00 s timestamp delta and 20.20 s stored duration (0.20 s difference, consistent with second-resolution timestamps versus sub-second monotonic timing)

No private credentials or public IP addresses are recorded here.

Physical Linux validation is complete for the supported generic Linux and FRITZ!Box-enhanced paths tested above. OpenWrt, UniFi, MikroTik and other router-specific adapters remain future work rather than claimed integrations.