Add network-aware history and speed tests

[rsheyd]

Why

Brief connection problems are difficult to compare from memory alone. This change extends PingZilla's existing continuous latency history so a user can answer two questions with recorded evidence:

• Which connection was active at a particular time?
• How was that connection behaving?

The motivating case is comparing coffee-shop Wi-Fi with a personal hotspot when both occasionally exhibit short glitches.

What changed

Network-aware history

• Associates ping samples with network sessions based on the public IP and ISP fingerprint already available to PingZilla.
• Starts a new session after detected network changes, meaningful reconnects, and sufficiently long sleep gaps.
• Splits the historical line at session boundaries so the graph does not imply a latency spike between different connections.
• Gives known networks stable colors across sessions.
• Lets users assign a readable network name when SSID access is unavailable or restricted.
• Migrates existing persisted history into an unknown legacy session and continues retaining approximately 24 hours of data.

Interactive graph and session details

• Applies the selected 5m, 30m, 1h, or 24h statistics range to the historical graph.
• Makes latency points selectable and shows the timestamp, ping/timeout, session duration, median, average, p95, and packet loss.
• Preserves hover highlighting and point selection when speed-test markers are present.
• Uses standalone reference dots for speed-test markers so their one-point dataset does not take over Recharts tooltip indexing.

Short, optional speed tests

• Adds a user-triggered capacity test using the macOS-specific /usr/bin/networkQuality command.
• Records download and upload capacity with the active network session.
• Uses a seven-second default to limit time, data transfer, battery use, and disruption.
• Allows the duration to be configured from 3–30 seconds.
• Shows a countdown while the test is running and displays the result at its recorded local time.
• Includes a signed-bundle smoke-test entry point for validating networkQuality availability.

Shutdown and contributor workflow

• Defers shutdown out of the native menu callback, persists current state, and guards against duplicate Quit requests.
• Preserves native tray menu items and updates their labels in place, avoiding menu replacement while AppKit processes user interactions.
• Rebuilds the tray menu only when site monitors are added or removed.
• Adds local development, validation, production-bundle, ad-hoc signing, and manual testing instructions.

Screenshot

Validation

• pnpm build
• cargo fmt --check --manifest-path src-tauri/Cargo.toml
• cargo test --manifest-path src-tauri/Cargo.toml — 7 tests passed
• Full pnpm tauri build completed successfully and produced both the macOS app and DMG.
• Interactive browser regression test with 30 minutes of fixture history and a recorded speed test:
  • hover highlighting moved between latency points
  • distinct points were selectable in both 5m and 30m ranges
  • selecting the speed-test marker displayed its associated result
• Manual development-app testing covered the network-name editor, speed-test countdown, graph selection, and Quit behavior.
• Production bundle built with pnpm tauri build --bundles app, ad-hoc signed with src-tauri/Entitlements.plist, and verified with codesign --verify --deep --strict.
• Manual testing in that signed production bundle confirmed:
  • the seven-second speed-test countdown and sandboxed networkQuality execution
  • saved download/upload results and a selectable graph marker
  • hover highlighting and distinct point selection in both 5m and 30m ranges after a speed test
  • network naming
  • history, network names, and speed-test persistence after relaunch
  • clean shutdown from the native Quit menu without a crash
  • Wi-Fi ↔ hotspot transition detection

Additional release checks

The following transitions would still benefit from broader testing before release:

• sleep/wake and meaningful reconnects
• VPN transitions
• migration from older persisted history

networkQuality is intentionally treated as a macOS-specific first implementation. The backend should be revisited if packaging, sandboxing, or Mac App Store review makes direct invocation unsuitable.