Share sccache between manual dev builds and CI

SCCACHE_DIR/CARGO_TARGET_DIR now point at /var/local/sccache and
/var/local/cargo-target, shared with the interactive dev shell via a
new `builders` group, instead of the CI job hitting a leftover
personal sccache server it had no permission to write build output for.

.gitea/workflows/deploy.yml

@@ -15,6 +15,11 @@ jobs:
       CARGO_HOME: /var/local/cargo
       RUSTUP_HOME: /var/local/rustup
       PATH: /var/local/cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/bin
+      # Shared with interactive dev builds (see ~/.config/fish/config.fish)
+      # so a crate compiled once, by either a manual build or CI, is
+      # cached for the other - real cache hits, not just a warm toolchain.
+      SCCACHE_DIR: /var/local/sccache
+      CARGO_TARGET_DIR: /var/local/cargo-target
     steps:
       - uses: actions/checkout@v4
 
@@ -26,8 +31,8 @@ jobs:
           set -euo pipefail
           rel="/srv/app/uhhm-portal/releases/${{ github.sha }}"
           mkdir -p "$rel"
-          cp target/release/portal "$rel/uhhm-portal"
-          cp -r target/site "$rel/site"
+          cp "$CARGO_TARGET_DIR/release/portal" "$rel/uhhm-portal"
+          cp -r "$CARGO_TARGET_DIR/site" "$rel/site"
           ln -sfn "$rel" /srv/app/uhhm-portal/current
 
       # Sourced from this repo's own Settings -> Actions Variables/Secrets,