Fix uploads over 4 GB failing with a misleading size error

Livewire's temporary upload rule was hard-coded to max:4194304 (4 GB),
so /livewire/upload-file rejected any larger file no matter how high
PHP_UPLOAD_MAX_FILESIZE or the admin's max file size were set.
_uploadErrored() then replaced Livewire's actual message with "file
exceeds the maximum size of N MB", quoting the admin limit the file was
under.

The cap is removed: PHP's upload_max_filesize is the hard limit and the
admin setting is still enforced in updatedFiles() and createShare(). A
rejected upload now logs the real validation errors and tells the user
the server could not accept the file.

max_upload_time is configurable via LIVEWIRE_MAX_UPLOAD_TIME, and the
README documents every limit large uploads depend on.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017XYnWFt9pJEwvAmNFN38XD

docker-compose.example.yml

@@ -59,6 +59,7 @@ services:
       # PHP_MAX_EXECUTION_TIME: "300"   # Upload timeout in seconds
       # PHP_MAX_INPUT_TIME: "300"       # Input processing timeout
       # PHP_MEMORY_LIMIT: "512M"        # PHP memory limit
+      # LIVEWIRE_MAX_UPLOAD_TIME: "30"  # Minutes a single upload may take (raise for large files on slow links)
     healthcheck:
       test: ["CMD", "curl", "--silent", "--fail", "http://localhost/up"]
       interval: 30s