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>

.gitea/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    container: archlinux:latest
+    steps:
+      - name: Prepare container
+        run: pacman -Syu --noconfirm --needed base-devel git rust dbus
+      - name: Checkout
+        uses: builtin:checkout
+      - name: Format, lint, build
+        run: |
+          cargo fmt --check
+          cargo clippy --locked --release -- -D warnings
+          cargo build --locked --release
+      - name: PKGBUILD and Cargo.toml agree
+        run: scripts/check-version