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/store.ts

@@ -42,7 +42,7 @@ export interface BootstrapStateModel {
   currentStage: string | null
   installRoot: string | null
   error: string | null
-  logs: Array<{ stage?: string; line: string }>
+  logs: Array<{ stage?: string; line: string; stream?: 'stdout' | 'stderr' }>
 }
 
 const INITIAL: BootstrapStateModel = {
@@ -106,6 +106,7 @@ interface BootstrapLogEvent {
   type: 'log'
   stage?: string
   line: string
+  stream?: 'stdout' | 'stderr'
 }
 
 interface BootstrapCompleteEvent {
@@ -192,7 +193,7 @@ export async function initialize(): Promise<void> {
         break
       }
       case 'log': {
-        const logs = [...cur.logs, { stage: payload.stage, line: payload.line }]
+        const logs = [...cur.logs, { stage: payload.stage, line: payload.line, stream: payload.stream }]
         // Keep the rolling buffer bounded so the UI doesn't get OOM'd
         // during a long install (playwright chromium download is ~10k lines).
         const trimmed = logs.length > 2000 ? logs.slice(-2000) : logs