Adds a build-time-configured transport reconnect hook so internal builds can recover the underlying transport (e.g. WARP VPN) before the relay reconnect, while OSS builds stay a pure no-op.
The generic "Reconnect to relay" button is transport-agnostic; internal users behind a VPN need the transport re-established first. A build-time env var `BUZZ_BUILD_RELAY_RECONNECT_CMD` (set only in `squareup/buzz-releases`) carries a JSON config validated into a typed Rust struct at compile time, so the OSS binary ships with zero VPN knowledge.
- New Tauri command `relay_reconnect_hook` runs structured fixed-argv steps plus a readiness probe, wrapped in `tokio::task::spawn_blocking`; non-fatal end-to-end so any failure falls through to `preconnect()`.
- `ReconnectHookConfig` lives in one dep-free source file `include!`'d by both `build.rs` and the runtime command, so the compile-time validation and runtime parse cannot drift.
- `useReconnectRelay.ts` invokes the hook before relay preconnect, guarded so a hook rejection cannot abort the reconnect.
- When `BUZZ_BUILD_RELAY_RECONNECT_CMD` is unset (OSS), the command compiles to an early-return no-op.
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>
Co-authored-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@sprout-oss.stage.blox.sqprod.co>
