Timestamped output folders to prevent report overwrites

[timini]

Problem

Currently all pipeline runs write to results/ (single mode) or results/auto/ (auto/fullauto mode), overwriting previous results. This makes it easy to lose earlier runs.

Proposed Fix

1. Timestamped output folders: Default params.outdir to include a timestamp, e.g. results/2026-03-05_14-30-00/ or results/auto_500-8kHz_2026-03-05/
2. Clean up existing results/: tidy up any accumulated artifacts from previous runs
3. Optional: add a --run-label param so users can name runs (e.g. --run-label mid-horn-test)
4. Symlink results/latest to the most recent run for convenience

Current Behavior

• results/ and results/auto/ get overwritten each run
• No way to compare runs side-by-side without manually copying outputs

Desired Behavior

• Each run gets its own directory
• Previous results are preserved
• Easy to find the latest run via symlink