feat(packaging): pre-spawn cleanup wrapper for clean restarts

Symptom: each app restart that didn't go through Stop daemon left
an orphan mycelium running as root, claiming the TUN \"mycelium\",
UDP/9650 (multicast discovery) and TCP/8990 (JSON-RPC, hardcoded
in 0.6.1 — no flag). Subsequent starts panicked with EBUSY or
\"Address in use\" on whichever port the orphan held.

We can't SIGKILL the orphan from user-space (root process). Move
the cleanup into an elevated context that runs in the same pkexec
authentication as the daemon spawn:

  /usr/bin/mycellium-bootstrap   (new shell script in the .deb)
    pkill -9 -x mycelium
    ip link del mycelium / mycel0
    exec /usr/bin/mycelium \"\$@\"

The polkit policy now annotates this exact path with
auth_admin_keep so a single password prompt covers every
subsequent restart in the user's session.

Sidecar: when /usr/bin/mycellium-bootstrap exists (production
install) we hand pkexec that path instead of the bare daemon.
\`pnpm tauri dev\` falls back to the unwrapped binary path.

release/SHA256SUMS

@@ -1 +1 @@
-acab8758c4ba7f3894e5e9bce28cbd759b8ec7e08a1ee00f54f6fdcac75a4221  release/mycellium-ui_0.1.0_amd64.deb
+38e0a3d03797490e1d6caa2681f9d5580493908834736b0db6a7d99558bb8823  release/mycellium-ui_0.1.0_amd64.deb