Drop the log.Printf/fmt.Printf traces that fired on every config/input/
click/scroll/open/worker-result during IME and tap debugging. These were
noise (and some were commented out). Error, limit, and recovery logs are
kept; the default-off profiler and gated IME debug remain untouched.
- Initialize browser path to the actual startup directory instead of '/'
- Improve '..' navigation to be relative to the filesystem root
- Fix path duplication issues by avoiding redundant absolute path joining
- Fix ChunkedBuffer.Insert to always update file length.
- Fix UpdateLineIndexAfterEdit to not shift the first line offset.
- Remove redundant ReadFileTask dispatch in HandleBrowserTap.
- Add end-to-end test for typing at start of buffer.
