feat: deep linking for hosted URLs and openconcho:// scheme

Add /explore redirect route that maps Honcho's deep-link shape
(?workspace=...&view=...&session=...) onto our existing flat routes,
so any app.honcho.dev URL works against a self-hosted instance by
swapping the host.

Wire tauri-plugin-deep-link to register the openconcho:// scheme on
desktop and forward incoming URLs into the router on launch and at
runtime.

packages/desktop/src-tauri/Cargo.toml

@@ -14,5 +14,6 @@ tauri-build = { version = "2", features = [] }
 tauri = { version = "2", features = [] }
 tauri-plugin-http = "2"
 tauri-plugin-shell = "2"
+tauri-plugin-deep-link = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"