presence: BLE proximity events for a kiosk screen

A swayidle-shaped daemon: `present <cmd>` runs when a Bluetooth LE device
comes within an RSSI threshold, `absent <secs> <cmd>` once nobody has for
that long. Near means 3 of the last 5 advertisements at or above -58 dBm by
default; --calibrate prints the raw stream so the threshold is picked at the
installed screen, not guessed. Nothing is stored: a few seconds of samples in
memory, counted.

Packaged for the [uhhm] registry from the checkout itself, built natively per
arch on tag by Gitea Actions, with the version checked across Cargo.toml,
PKGBUILD and the tag.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

scripts/check-version

@@ -0,0 +1,13 @@
+#!/bin/bash
+# check-version [tag-version]: PKGBUILD pkgver, Cargo.toml version and, when
+# given, the tag must all be the same string. Version lives in Cargo.toml;
+# PKGBUILD mirrors it so makepkg needs no VCS pkgver().
+set -euo pipefail
+cd "$(dirname "$0")/.."
+cargo=$(sed -n 's/^version = "\(.*\)"/\1/p' Cargo.toml | head -1)
+pkg=$(sed -n 's/^pkgver=//p' PKGBUILD)
+[ "$cargo" = "$pkg" ] || { echo "Cargo.toml $cargo != PKGBUILD pkgver $pkg" >&2; exit 1; }
+if [ $# -gt 0 ]; then
+    [ "$1" = "$cargo" ] || { echo "tag $1 != version $cargo" >&2; exit 1; }
+fi
+echo "version $cargo"

scripts/publish-registry

@@ -0,0 +1,19 @@
+#!/bin/bash
+# publish-registry <dir>: upload every built package in <dir> (debug packages
+# skipped) to the [uhhm] Gitea Arch registry. HTTP 409 means that
+# pkgver-pkgrel is already published, which is fine on re-runs.
+set -euo pipefail
+: "${REGISTRY_TOKEN:?}" "${REGISTRY_URL:?}"
+shopt -s nullglob
+pkgs=("$1"/*.pkg.tar.{zst,xz,gz})
+[ ${#pkgs[@]} -gt 0 ] || { echo "no packages in $1" >&2; exit 1; }
+for pkg in "${pkgs[@]}"; do
+    case "$pkg" in *-debug-*) continue ;; esac
+    code=$(curl -sS -o /tmp/registry-resp -w '%{http_code}' \
+        --user "bl:$REGISTRY_TOKEN" --upload-file "$pkg" "$REGISTRY_URL")
+    case "$code" in
+        2??) echo "uploaded $(basename "$pkg")" ;;
+        409) echo "already published: $(basename "$pkg")" ;;
+        *)   echo "::error::$(basename "$pkg"): HTTP $code"; cat /tmp/registry-resp; exit 1 ;;
+    esac
+done