Scraping resilience, metadata tooling, and repository hygiene

Consolidates mosaic and session hardening (login retry, skip processed scans, no retry on 404, started_at), progress reporting (Markdown tables, by-year rollup, rolling-window rate/ETA), and metadata workflow scripts (run_metadata_scan.sh, scan_progress_report.py, export_machine_metadata.py). Adds mosaic reconstruction sample JPEGs referenced by the report. Updates .gitignore for backup/ and .claude/; sample_random_scans helper is documented for branch testing/sample-runs only (see README).

run_metadata_scan.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+VENV="/tmp/spruce_venv"
+
+if [[ ! -x "$VENV/bin/python" ]]; then
+    echo "Setting up venv at $VENV..."
+    python3 -m venv "$VENV"
+    "$VENV/bin/python" -m ensurepip --upgrade
+    "$VENV/bin/pip" install -q -r "$SCRIPT_DIR/requirements.txt"
+fi
+
+echo "Starting metadata-only scan of all machines..."
+"$VENV/bin/python" "$SCRIPT_DIR/scraper.py" --metadata-only "$@"