docs(headless-server): fix package list, extraction perms, and ldd command

Three fixes to the headless Linux server guide, each of which stops a
first-time setup from working.

The prerequisite list installed only CLI tools and Xvfb, none of the
shared libraries Electron links against. On a minimal server or
container image `orca serve` then fails before Electron starts. Adds the
library set, plus the unsuffixed package names for releases that predate
the 64-bit time_t transition.

The guide tells you to run --appimage-extract and, separately, to run
the service as a dedicated non-root user with the install directory
root-owned. Those two halves combine badly: extraction leaves
squashfs-root as drwx------, so the service user cannot traverse it, and
chmod 755 /opt/orca does not reach inside. Adds the missing chmod to
both places.

The troubleshooting step said to run `ldd squashfs-root/orca`. The
Electron binary is orca-ide, and ldd on a path that does not exist
prints nothing and exits cleanly — a clean-looking result in exactly the
situation where you are hunting a missing library.

docs/reference/headless-linux-server.md

@@ -17,13 +17,37 @@ differ on other Debian-derived releases.
 
 ## Ubuntu and Debian prerequisites
 
-Install the AppImage runtime dependency and Xvfb:
+Install the CLI tools, Xvfb, and the shared libraries Electron links against.
+A minimal server or container image ships none of the Electron libraries, and
+`orca serve` then fails before Electron starts:
 
 ```bash
 sudo apt-get update
-sudo apt-get install -y curl file jq xvfb zlib1g-dev
+sudo apt-get install -y \
+  curl file jq xvfb zlib1g-dev ca-certificates git \
+  libgtk-3-0t64 libnss3 libatk1.0-0t64 libatk-bridge2.0-0t64 libgbm1 libasound2t64 \
+  libxtst6 libcups2t64 libdrm2 libxkbcommon0 libpango-1.0-0 libcairo2 libatspi2.0-0t64 \
+  libxcomposite1 libxdamage1 libxfixes3 libxrandr2 libxrender1 libx11-xcb1 \
+  libxcb-dri3-0 libxss1
 ```
 
+That command is for Ubuntu 24.04 and newer and Debian 13 and newer. Those
+releases carried out the 64-bit `time_t` transition, which renamed six of the
+packages with a `t64` suffix. On Ubuntu 20.04, Ubuntu 22.04, and Debian 12,
+substitute the unsuffixed names:
+
+- `libgtk-3-0t64` becomes `libgtk-3-0`
+- `libatk1.0-0t64` becomes `libatk1.0-0`
+- `libatk-bridge2.0-0t64` becomes `libatk-bridge2.0-0`
+- `libasound2t64` becomes `libasound2`
+- `libcups2t64` becomes `libcups2`
+- `libatspi2.0-0t64` becomes `libatspi2.0-0`
+
+The other names are identical on every supported release. The two sets are not
+interchangeable: `apt-get install` fails outright on a name the release does not
+carry, and on Ubuntu 24.04 `libasound2` survives only as a virtual package for an
+unrelated library, so it installs without giving Electron what it needs.
+
 On Ubuntu 22.04, install `libfuse2` to execute the AppImage through FUSE. On
 Ubuntu 24.04 and Debian, the equivalent package may be `libfuse2t64`. FUSE is
 optional: without it, use the AppImage's supported extraction path:
@@ -31,9 +55,15 @@ optional: without it, use the AppImage's supported extraction path:
 ```bash
 cd /opt/orca
 ./orca-linux.AppImage --appimage-extract
+sudo chmod -R a+rX /opt/orca/squashfs-root
 /opt/orca/squashfs-root/AppRun serve --port 6768
 ```
 
+The `chmod` is required whenever the extraction runs as a different user than
+the server: `--appimage-extract` creates `squashfs-root` as `drwx------` owned by
+the extracting user, so anyone else — including a dedicated service user — cannot
+even traverse it, and the run fails before Electron starts.
+
 Docker commonly has no FUSE device. Use `--appimage-extract` once or
 `--appimage-extract-and-run`; neither requires a privileged container. The
 extract-and-run wrapper can print extracted paths before Orca starts, so
@@ -144,8 +174,15 @@ AppImage, but must not be able to replace it or the rollback artifacts.
 sudo useradd --system --create-home --shell /usr/sbin/nologin orca
 sudo chown root:root /opt/orca /opt/orca/orca-linux.AppImage
 sudo chmod 755 /opt/orca /opt/orca/orca-linux.AppImage
+# Only if you ran --appimage-extract: extraction leaves squashfs-root root-only.
+sudo chmod -R a+rX /opt/orca/squashfs-root
 ```
 
+The last line matters because the two halves of this guide combine badly without
+it. `--appimage-extract` writes `squashfs-root` as `drwx------ root root`, so the
+`orca` service user cannot read or traverse the extracted tree and the unit fails
+at startup. `chmod 755 /opt/orca` alone does not reach into it.
+
 For most hosts, one `orca serve` service is enough because Orca starts Xvfb on
 display `:99` when no display exists:
 
@@ -834,7 +871,8 @@ refuse to run there and print the command to run on the machine you want.
 - GPU or DRI warnings on a VPS: keep `LIBGL_ALWAYS_SOFTWARE=1` in the service
   environment.
 - Chromium sandbox errors: confirm the service is running as the non-root
-  `orca` user and that `/opt/orca` is readable by that user.
+  `orca` user and that `/opt/orca` is readable by that user, including
+  `/opt/orca/squashfs-root` if you extracted the AppImage.
 - Clients cannot connect: make sure `--pairing-address` is an address reachable
   from the client, and make sure firewalls allow the selected `--port`.
 - Journal shows `Another Orca instance is already running for this userData
@@ -857,4 +895,7 @@ profile` and the unit exits `3`: another process already owns the profile, so
   `sudo systemctl reset-failed orca-serve.service` first.
 - Diagnosing other missing libraries: extract the AppImage without launching it
   with `./orca-linux.AppImage --appimage-extract`, then run
-  `ldd squashfs-root/orca` to list any shared libraries the host is missing.
+  `ldd squashfs-root/orca-ide` to list any shared libraries the host is missing.
+  The Electron binary is `orca-ide`, not `orca`; `ldd` on a path that does not
+  exist prints nothing and exits cleanly, which reads as a clean result in
+  exactly the situation where you are hunting a missing library.