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).

spruce/progress.py

@@ -5,6 +5,7 @@ Progress tracking (JSON) and CSV writing.
 import csv
 import json
 import logging
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Iterator
 
@@ -27,6 +28,7 @@ class ProgressTracker:
     def __init__(self, path: Path) -> None:
         self.path = path
         self._done: set[str] = set()
+        self.started_at: str = datetime.now(timezone.utc).isoformat()
         self._load()
 
     def _load(self) -> None:
@@ -34,6 +36,8 @@ class ProgressTracker:
             try:
                 data = json.loads(self.path.read_text())
                 self._done = set(data.get("completed_urls", []))
+                if "started_at" in data:
+                    self.started_at = data["started_at"]
                 log.info("Resuming: %d URLs already downloaded.", len(self._done))
             except Exception:
                 log.warning("Could not read progress file; starting fresh.")
@@ -59,7 +63,10 @@ class ProgressTracker:
         self.path.parent.mkdir(parents=True, exist_ok=True)
         tmp = self.path.with_suffix(".json.tmp")
         tmp.write_text(
-            json.dumps({"completed_urls": sorted(self._done)}, indent=2)
+            json.dumps(
+                {"started_at": self.started_at, "completed_urls": sorted(self._done)},
+                indent=2,
+            )
         )
         tmp.replace(self.path)  # atomic on POSIX; avoids corrupt JSON on crash