fork: initialize Mycellium UI Private from Mycell-UI@5229e2c

This repo is a hard fork of mycellium-ui dedicated to the
mycelium-private experimental track upstream. The two apps coexist
on the same machine via distinct app identifiers, polkit actions,
and binary names.

Renames
- package + crate: mycellium-ui → mycellium-ui-private
- bundle identifier: tech.threefold.mycellium-ui-private
- daemon binary: mycelium-private (separate upstream release tarball)
- bootstrap wrapper: /usr/bin/mycellium-bootstrap-private
- polkit policy file + action id

Functional changes
- SidecarConfig.network_name field (UTF-8, 2..=64 bytes)
- start() refuses to spawn without a network name AND a 32-byte
  key file at app_data_dir/network_key.bin; surfaces a clear
  error rather than letting mycelium-private fail mid-startup
- network_key_status / generate / import / export / delete
  commands; uses OS RNG (rand) and writes 0600
- empty default peers list (no Threefold seed for private overlays)
- new Settings → Private network panel: name input, key generate /
  reveal-hex / import / delete, status indicator

Adapted bootstrap script kills both `mycelium` and
`mycelium-private` orphans (cross-clash on UDP/9650 + TCP/8990).

CI workflow + sidebar branding updated. The README explains the
divergence model and how to cherry-pick upstream fixes.

release/SHA256SUMS

@@ -1 +1 @@
-38e0a3d03797490e1d6caa2681f9d5580493908834736b0db6a7d99558bb8823  release/mycellium-ui_0.1.0_amd64.deb
+fe9e98ff6b2ee740345a9cac5bc1fd828cf7b53c96242c0c15fdc26dd8249b4e  release/mycellium-ui-private_0.1.0_amd64.deb