docs: percantik halaman repo — badge lengkap + diagram alur di README, template issue laporan hardware, CONTRIBUTING, SECURITY, dan kartu social preview

SECURITY.md

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+# Security
+
+This is a small local tool. The relevant surface:
+
+- It writes 64-byte HID reports to the panel matching `VID 0x5131 / PID 0x2007`
+  (plus a udev rule that grants the logged-in user access to that `hidraw` node).
+- The tray app runs `systemctl --user` and, for the udev rule, `pkexec sh` on a script it
+  writes to `/tmp`. Nothing else is executed, and no data leaves the machine.
+- No secrets are stored. The config file (`~/.config/gamemax-report/config.json`) holds
+  sensor channel names and display settings only.
+
+If you find a problem — for example a way to make the helper scripts run something else,
+or a path that writes outside the documented locations — please open an issue (or a
+private security advisory on GitHub). Do not test on hardware you do not own.