poi-index: generalize poi-extract docs/units (drop host/username specifics)

Remove ullrich.is / 1.8 TB / hardcoded 'trails' username assumptions from the
poi-extract README and service unit; refer to 'the pipeline user' and $USER /
%h instead so the docs serve self-hosters too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/brouter-host/poi-extract/README.md

@@ -5,9 +5,9 @@ Monthly job that turns an OSM PBF into the compact POI artifact the flagship's
 half of the [`poi-index`](../../../openspec/changes/poi-index/) change — it
 replaces the third-party Overpass dependency for the Planner's POI overlays.
 
-Runs on the dedicated BRouter host (`ullrich.is`, the box with 1.8 TB free)
+Runs on the BRouter host as a non-root user (docker-group rights, no sudo). The
-under the non-root `trails` user. The flagship import job
+flagship import job (`infrastructure/scripts/poi-import.sh`) pulls the result
-(`infrastructure/scripts/poi-import.sh`) pulls the result over the vSwitch.
+over the vSwitch.
 
 ## Files
 
@@ -49,18 +49,18 @@ artifact is unreachable from the public internet.
 ## Prerequisites
 
 - **Docker** — osmium runs in a container (`osmium.Dockerfile`, built on first
-  use as `trails-osmium:local`). The BRouter host's `trails` user is non-root
+  use as `trails-osmium:local`). The pipeline's user is non-root with no sudo,
-  with no sudo, so osmium can't be apt-installed; docker-group rights cover it.
+  so osmium can't be apt-installed; docker-group rights cover it. On Linux this
-  On Linux this adds no meaningful overhead — big files are bind-mounted, so I/O
+  adds no meaningful overhead — big files are bind-mounted, so I/O is native.
-  is native.
 - **On the host** (already present): `python3`, `curl`, `gzip`, `sha256sum`.
 
 ## Install the timer
 
-Deployed under `~trails/brouter/poi-extract/`. As a user unit with lingering:
+Deployed under the pipeline user's `~/brouter/poi-extract/`. As a user unit with
+lingering (so the timer runs even when nobody is logged in):
 
 ```bash
-loginctl enable-linger trails
+loginctl enable-linger "$USER"
 mkdir -p ~/.config/systemd/user
 cp poi-extract.service poi-extract.timer ~/.config/systemd/user/
 systemctl --user daemon-reload

infrastructure/brouter-host/poi-extract/poi-extract.service

@@ -1,8 +1,8 @@
 # POI extract — one-shot unit driven by poi-extract.timer. Runs as the
-# non-root `trails` user (docker-group, scoped to ~trails/brouter/). Install as
+# non-root pipeline user (docker-group rights, no sudo). Install as a user unit:
-# a user unit: `systemctl --user enable --now poi-extract.timer` with lingering
+# `systemctl --user enable --now poi-extract.timer` with lingering enabled
-# enabled (`loginctl enable-linger trails`), or as a system unit with
+# (`loginctl enable-linger "$USER"`), or as a system unit with User=<that user>.
-# User=trails. See README.md.
+# See README.md.
 [Unit]
 Description=Filter an OSM PBF to trails.cool POI categories and publish the artifact
 Wants=network-online.target
@@ -10,7 +10,7 @@ After=network-online.target
 
 [Service]
 Type=oneshot
-# Adjust WorkingDirectory to the deployed path (e.g. /home/trails/brouter/poi-extract).
+# %h resolves to the running user's home; adjust if deployed elsewhere.
 WorkingDirectory=%h/brouter/poi-extract
 ExecStart=%h/brouter/poi-extract/poi-extract.sh
 # The planet download + filter is long-running and IO-heavy; give it room and