decodeURIComponent throws on '%' not followed by two hex digits. The two
calls inside parseAssistantFileLink and normalizeFileUrlPath had no
try/catch, so any timeline message containing strings like '100% packet
loss' (ping output), '%PATH%' or '0% off' could escape into the React
tree and unmount the agent route, leaving the renderer blank.
Wrap both calls in a local safeDecodeURIComponent that returns the input
unchanged when decoding fails, mirroring the helper already used in
host-routes.ts.
Closes#1148
