Restructure documentation, validate metadata removal, consolidate assets

data/README.md

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+# Repository data
+
+Tracked data is organized by purpose:
+
+```text
+data/
+  fixtures/
+    provenance/   Real format and provenance fixtures used by tests
+  calibration/
+    <vendor>/     Minimal controlled inputs needed to rebuild detector assets
+  synthid/
+    originals/    Canonical provider-oracle fixtures, stored once
+    manifest.csv  Provenance and verification record for each original
+    full-pipeline-quality.csv
+                  Reusable full-pipeline evaluation selection
+  evaluations/
+    fidelity/     Evaluation instructions and hand-verified ground truth
+```
+
+## Storage rules
+
+1. Store each binary image once. Evaluation manifests and documentation point
+   to its canonical location.
+2. Put executable test fixtures in `fixtures/`.
+3. Put only the minimal reproducible detector inputs in `calibration/`.
+4. Put externally verified SynthID originals in `synthid/originals/` and keep
+   both CSV files synchronized.
+5. Keep evaluation outputs outside the repository. Record reproducible
+   commands, hashes, and oracle verdicts instead of committing another corpus
+   copy. A small curated before-and-after example may live in `docs/images/`
+   when it is part of the public documentation.
+6. Runtime detector assets belong in `src/remove_ai_watermarks/assets/`.
+   Unregistered research candidates belong in
+   `scripts/assets/visible-mark-candidates/` so they are not shipped in the
+   wheel.
+
+The source distribution excludes `data/`; the wheel contains only package
+runtime assets.