docs: scrub dangling references to deleted roadmap docs

The ROADMAP/ROADMAP-PINCHFLAT docs were removed; this drops the now-dead
"see ROADMAP-PINCHFLAT.md" breadcrumbs (and one "the roadmap" mention)
from source comments, preserving the surrounding Pinchflat-style context.
Comment-only; typecheck (node+web) green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/ipc.ts

@@ -251,7 +251,7 @@ export function registerIpcHandlers(getMainWindow: () => BrowserWindow | null):
     return result
   })
 
-  // --- Media-manager sources (Pinchflat-style index; see ROADMAP-PINCHFLAT.md) ---
+  // --- Media-manager sources (Pinchflat-style index) ---
   ipcMain.handle(IpcChannels.sourcesList, () => listSources())
   ipcMain.handle(IpcChannels.sourceItems, (_e, sourceId: string) => listMediaItems(sourceId))
   ipcMain.handle(IpcChannels.sourceRemove, (_e, id: string) => removeSource(id))