Document session log contents (log file header + developer website page)

[Gero1999]

Enhancement

The exported session_log.txt has no explanation of what it contains, what log levels mean, or what is/isn't captured. Users opening the file have no context.

Scope

1. Log file header

Add a brief header block at the top of session_log.txt (written by .export_session_log()) explaining:

• What the log captures (app events, not raw R console)
• What is NOT captured (uncaught warnings/errors from dependencies)
• Current log level threshold and how to change it
• Link to the developer documentation page for full reference

2. Developer website page

Add a page under the Developers section of the aNCA pkgdown website with:

• A table of all currently logged events organized by workflow stage
• Explanation of log levels (TRACE, DEBUG, INFO, SUCCESS, WARN, ERROR)
• How to configure the log level via aNCA_LOG_LEVEL
• What the log file does and does not capture

Depends on

• feat: replace logger with lightweight console logging + ZIP export #1212 (replace logger with console logging)