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

README.md

@@ -86,6 +86,19 @@ Migrations run automatically on startup. Open your configured domain — the Set
 | `caddy_data` | `/data` | TLS certificates |
 | `caddy_config` | `/config` | Caddy configuration |
 
+**Large files:**
+
+Uploads beyond the defaults need these limits raised together:
+
+| Limit | Where | Default |
+|-------|-------|---------|
+| `PHP_UPLOAD_MAX_FILESIZE` / `PHP_POST_MAX_SIZE` | Environment | `4G` — hard cap per file / per upload batch |
+| Max file size / Max size per share | Admin → Settings | 100 MB / 2 GB |
+| `LIVEWIRE_MAX_UPLOAD_TIME` | Environment | 30 minutes per upload |
+| `OCTANE_MAX_EXECUTION_TIME` / `PHP_MAX_EXECUTION_TIME` | Environment | 300 seconds — encrypting a large file takes a while |
+
+Behind a reverse proxy, raise its request body limit and read timeout as well (nginx: `client_max_body_size`, `proxy_read_timeout`).
+
 ### Manual (without Docker)
 
 ```bash