feat(packaging): ship punktfunk everywhere, and deprecate the session's stray pairing flag

The rest of C1. A CLI that only exists in a dev tree is not a door anyone can use, so it
now builds and installs in deb, rpm, arch, nix, flatpak and MSIX alongside the client and
the session. On Windows it gets its own `AppListEntry="none"` application with the alias
`punktfunk.exe` — a command, not a Start-menu tile — which is what the Playnite importer
will shell to for `punktfunk library <host> --json`.

`punktfunk-session --pair` prints a deprecation notice and forwards. Pairing is a trust
ceremony and belongs to the brain, fronted by `punktfunk pair` or a shell; a renderer
owning one is precisely the mixing of concerns this split exists to undo. It keeps working
for a release, because someone's provisioning script is calling it today.

Decky's invocations are untouched and verified still working (`--list-hosts` JSON shape
unchanged, `--reachable` exit codes unchanged): those flags are a frozen compat contract
until Decky migrates to the verbs at its own pace.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packaging/debian/build-client-deb.sh

@@ -38,9 +38,11 @@ BIN="$OUTDIR/$PKG"
 # The Vulkan/Skia session streamer the shell execs for a connect — shipped alongside the shell
 # (the shell resolves it as its /usr/bin sibling), or desktop streaming breaks.
 SESSION_BIN="$OUTDIR/punktfunk-session"
+# The headless CLI (design/client-architecture-split.md §4) ships with every client.
+CLI_BIN="$OUTDIR/punktfunk"
 if [ ! -x "$BIN" ] || [ ! -x "$SESSION_BIN" ]; then
   echo "==> building $CRATE + punktfunk-client-session (release${TARGET:+ for $TARGET})"
-  cargo build --release --locked "${CARGO_TARGET_ARGS[@]}" -p "$CRATE" -p punktfunk-client-session
+  cargo build --release --locked "${CARGO_TARGET_ARGS[@]}" -p "$CRATE" -p punktfunk-client-session -p punktfunk-cli
 fi
 
 STAGE="$(mktemp -d)"
@@ -50,6 +52,7 @@ DOCDIR="$STAGE/usr/share/doc/$PKG"
 # --- file layout --------------------------------------------------------------
 install -Dm0755 "$BIN"                                   "$STAGE/usr/bin/$PKG"
 install -Dm0755 "$SESSION_BIN"                           "$STAGE/usr/bin/punktfunk-session"
+install -Dm0755 "$CLI_BIN"                               "$STAGE/usr/bin/punktfunk"
 install -Dm0644 packaging/linux/io.unom.Punktfunk.desktop \
                 "$STAGE/usr/share/applications/io.unom.Punktfunk.desktop"
 # DualSense hidraw access (full pad fidelity through SDL's HIDAPI driver).