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.

src-tauri/Cargo.toml

@@ -1,13 +1,13 @@
 [package]
-name = "mycellium-ui"
+name = "mycellium-ui-private"
 version = "0.1.0"
-description = "Mycelium overlay network desktop client"
+description = "Mycelium private network desktop client"
 authors = ["syoul"]
 edition = "2021"
 rust-version = "1.77"
 
 [lib]
-name = "mycellium_ui_lib"
+name = "mycellium_ui_private_lib"
 crate-type = ["staticlib", "cdylib", "rlib"]
 
 [build-dependencies]
@@ -27,6 +27,8 @@ tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 portpicker = "0.1"
 parking_lot = "0.12"
+rand = "0.8"
+hex = "0.4"
 
 [features]
 custom-protocol = ["tauri/custom-protocol"]