fix(upload): plain-language upload failure text instead of the raw MatrixError (#213)

The upload card printed the SDK's toString — 'MatrixError: [413] nope
(http://<hs>/_matrix/media/v3/upload?filename=…)'. describeUploadError() maps
the common cases to one sentence: 413/M_TOO_LARGE → 'This file is larger than
the server allows (limit N)' using m.upload.size when known, 429 → 'Slow down —
try again in a moment.', 401/403 → 'The server refused this upload: <server
text>', 5xx/transport after the retry loop → 'Couldn't reach the server. Check
your connection and retry.', other 4xx → the server's own sentence, URL
stripped. Both card renderers use it; the raw error is still console.warn-ed
by uploadContent for debugging. Unit-tested; verified headless with routed
413/403/503 responses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/upload-card/CompactUploadCardRenderer.tsx

@@ -6,6 +6,7 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { TUploadContent } from '../../utils/matrix';
 import { bytesToSize, getFileTypeIcon } from '../../utils/common';
 import { useMediaConfig } from '../../hooks/useMediaConfig';
+import { describeUploadError } from '../../utils/uploadError';
 
 type CompactUploadCardRendererProps = {
   isEncrypted?: boolean;
@@ -91,7 +92,7 @@ export function CompactUploadCardRenderer({
           )}
           {upload.status === UploadStatus.Error && (
             <UploadCardError>
-              <Text size="T200">{upload.error.message}</Text>
+              <Text size="T200">{describeUploadError(upload.error, allowSize)}</Text>
             </UploadCardError>
           )}
           {upload.status === UploadStatus.Idle && fileSizeExceeded && (

src/app/components/upload-card/UploadCardRenderer.tsx

@@ -24,6 +24,7 @@ import {
 } from '../../state/room/roomInputDrafts';
 import { useObjectURL } from '../../hooks/useObjectURL';
 import { useMediaConfig } from '../../hooks/useMediaConfig';
+import { describeUploadError } from '../../utils/uploadError';
 import { compressImage, formatFileSize, isCompressible } from '../../utils/imageCompression';
 
 type PreviewImageProps = {
@@ -389,7 +390,7 @@ export function UploadCardRenderer({
           )}
           {upload.status === UploadStatus.Error && (
             <UploadCardError>
-              <Text size="T200">{upload.error.message}</Text>
+              <Text size="T200">{describeUploadError(upload.error, allowSize)}</Text>
             </UploadCardError>
           )}
           {upload.status === UploadStatus.Idle && fileSizeExceeded && (