fix(installer): stop mislabeling stdout-style progress as stderr

Both installers (Electron bootstrap-runner + Tauri) hardcoded a literal
`stderr: ` prefix onto every line that arrived on fd 2. Tools like
uv/pip/git/npm write normal progress to stderr by design, so routine
install output showed up tagged as "stderr" (and rendered red in the
Tauri progress UI), making a healthy install look like it was erroring.

Carry the stream as structured metadata (`stream: 'stdout' | 'stderr'`)
on the log event instead of mangling the line text. The UI now styles
stderr subtly (dimmed) rather than alarmingly, and the persistent
forensic logs keep their stdout/stderr distinction.

apps/bootstrap-installer/src-tauri/src/events.rs

@@ -51,6 +51,16 @@ pub enum StageState {
     Failed,
 }
 
+/// Which pipe a raw log line came from. Reported as structured metadata so
+/// the UI can style stderr subtly rather than mislabeling it as an error:
+/// uv/pip/git/npm write normal progress to stderr by design.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
+#[serde(rename_all = "lowercase")]
+pub enum LogStream {
+    Stdout,
+    Stderr,
+}
+
 /// The single event channel `bootstrap` emits these. `type` discriminates.
 #[derive(Debug, Clone, Serialize)]
 #[serde(tag = "type", rename_all = "lowercase")]
@@ -72,11 +82,14 @@ pub enum BootstrapEvent {
         #[serde(skip_serializing_if = "Option::is_none")]
         error: Option<String>,
     },
-    /// Raw stdout/stderr line from install.ps1 (or our wrapper).
+    /// Raw stdout/stderr line from install.ps1 (or our wrapper). `stream`
+    /// tells the UI which pipe it came from so stderr can be styled subtly
+    /// instead of being mislabeled as an error.
     Log {
         #[serde(skip_serializing_if = "Option::is_none")]
         stage: Option<String>,
         line: String,
+        stream: LogStream,
     },
     /// Sent once when all stages complete successfully.
     Complete {