Add debug log panel, median stats, recovery probe, and UI improvements

- Debug log: togglable panel with timestamped, level-tagged, color-coded
  entries (error/warning/notice/info/debug) from throughout the app
- Median latency: added to per-host stats and summary (min/med/avg/max)
- Recovery probe: rapid 500ms polling of 4 random hosts when hard offline,
  triggers normal tick as soon as connectivity returns
- Health status: multi-level (healthy/slow/degraded/offline) with
  hard-offline detection for recovery probe activation
- First tick discarded to avoid DNS/TLS cold-start latency skew
- Added Google, S3 ap-southeast-1 (Singapore) to monitored hosts
- UI: reduced row padding, larger sparkline canvas, bigger axis labels,
  pin icon hidden (but space preserved) for local network hosts
- Commit hash shown in footer via vite define plugin

vite.config.js

@@ -1,8 +1,16 @@
 import { defineConfig } from "vite";
 import tailwindcss from "@tailwindcss/vite";
+import { execSync } from "child_process";
+
+const commitHash = execSync("git rev-parse --short HEAD").toString().trim();
+const commitFull = execSync("git rev-parse HEAD").toString().trim();
 
 export default defineConfig({
     plugins: [tailwindcss()],
+    define: {
+        __COMMIT_HASH__: JSON.stringify(commitHash),
+        __COMMIT_FULL__: JSON.stringify(commitFull),
+    },
     build: {
         target: "esnext",
         minify: "esbuild",