fix(infra): Stalwart installer — repo rename + exact asset; flag 0.16 config break

- install.sh: default repo stalwartlabs/mail-server -> stalwartlabs/stalwart
  (renamed), and select the exact /stalwart-<target>.tar.gz asset excluding the
  foundationdb build (head -n1 could grab the wrong one).
- config.toml: $env{...} -> %{env:...}% (correct Stalwart macro syntax).

KNOWN ISSUE: Stalwart v0.16 removed TOML config (single config.json datastore +
everything else in the DB via CLI/UI), so this config.toml does not load on
0.16.8 ("Failed to parse data store settings"). Needs either a pinned pre-0.16
version or a migration to the v0.16 config model. Binary is installed; the
service is stopped pending that decision.

infrastructure/production/host/stalwart/install.sh

@@ -24,7 +24,7 @@ HOST_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
 CONFIG_FILE="${CONFIG_FILE:-$HOST_DIR/config.env}"
 
 PREFIX="/opt/stalwart"
-STALWART_REPO="${STALWART_REPO:-stalwartlabs/mail-server}"
+STALWART_REPO="${STALWART_REPO:-stalwartlabs/stalwart}"
 
 if [[ $EUID -ne 0 ]]; then
     error "Run as root."
@@ -67,7 +67,8 @@ else
 fi
 
 asset_url="$(curl -fsSL "$api" \
-    | grep -oE "https://[^\"]+${target}[^\"]+\.tar\.gz" \
+    | grep -oE "https://[^\"]+/stalwart-${target}\.tar\.gz" \
+    | grep -v foundationdb \
     | head -n1)"
 if [[ -z "$asset_url" ]]; then
     error "Could not find a ${target} .tar.gz asset in ${STALWART_REPO}@${STALWART_VERSION}."