Apply microSD write tweaks; correct docs: neon is on the built-in microSD slot

commit=30 on the root fs, journald capped at 100M, smartmontools disabled.
The neon root is a microSD card in the built-in slot (USB-attached reader),
not an external USB card; wording fixed across docs and the install script.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

NEON-CUSTOMIZATIONS.md

@@ -64,10 +64,11 @@ history show `nano /etc/default/grub` + `update-grub`): `GRUB_DEFAULT=0`,
 `GRUB_TIMEOUT=5`, `GRUB_TIMEOUT_STYLE=menu`,
 `GRUB_CMDLINE_LINUX_DEFAULT='splash'` (see `setup-i915-kernel7-fix.sh`).
 
-## Storage / wear on the USB-card root
+## Storage / wear on the microSD root
 
-neon's root is an external USB/SD card, so a few changes cut down writes
-and space use:
+neon's root is a microSD card in the built-in slot (`sda`; the slot's
+reader is USB-attached internally), and microSD handles lots of small
+writes poorly, so a few changes cut down writes and space use:
 - **`/tmp` is tmpfs** (in `/etc/fstab`:
   `tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0`). Not in the shell
   history, so it was probably added in the same `nano /etc/fstab` edit
@@ -79,6 +80,22 @@ and space use:
   install (`USE_DPKG`, `MANDELETE`). If another language's translations
   or man pages are ever needed, add them with
   `sudo dpkg-reconfigure localepurge`.
+- **Root mounted with `commit=30`** (2026-09-27): the root line in
+  `/etc/fstab` is `defaults,commit=30`; the pre-change copy is
+  `/etc/fstab.bak-2026-09-27`. ext4 commits its journal every 30s
+  instead of every 5s, so writes are batched into fewer, larger bursts.
+  Trade-off: a crash or forced power-off can lose up to ~30s of recent
+  changes that weren't fsync'd (apt/dpkg, editors and databases fsync, so
+  they're unaffected). 30 rather than 60 because this machine has needed
+  forced power-offs. `relatime` is kept deliberately (not `noatime`).
+- **journald capped at 100MB** (2026-09-27):
+  `/etc/systemd/journald.conf.d/50-max-size.conf` sets
+  `SystemMaxUse=100M` (it was 455MB).
+- **`smartmontools` disabled** (2026-09-27, `systemctl disable --now`):
+  it failed on every boot because neither the microSD card nor the eMMC
+  supports SMART.
+- The card doesn't support discard/TRIM (`lsblk -D` shows 0), so
+  `fstrim.timer` does nothing for it. That's harmless and was left alone.
 
 ## Networking