refactor: move the reference implementation to src/paperspec

The oracle had two import names, `tools.oracle` for the tools and
`paperspec` for other repositories, which could load the same code twice
in one process and needed a gate keyed on the module name. It now lives
in the standard src layout under its one name.

- git mv tools/oracle -> src/paperspec; the 22 rule modules are unchanged.
- The tools import `paperspec`. `tools/__init__.py` now holds the Python
  3.14 and cryptography/jsonschema check and puts src/ first on sys.path,
  so the tools run this checkout's code with or without pixi. The
  package's own __init__ checks nothing and exposes __version__.
- pyproject.toml: version from git tags via setuptools-scm
  (guess-next-dev, node-and-timestamp, src/paperspec/_version.py,
  gitignored). The packages stay listed rather than found because
  schemas/, sql/ and vectors/ stay at the root: the spec links to them and
  the site serves the schemas at their $id URLs.
- pixi.toml: a `dev` feature and environment with setuptools,
  setuptools-scm and python-build, and `pixi run -e dev wheel`.
- check.py scans src/paperspec for rule IDs; README, CONTRIBUTING, the
  FAQ, the overview, the vectors and tools READMEs and the changelog point
  at the new path. The FAQ no longer says the oracle is not a library.

pixi.lock is not re-solved in this commit: with a dynamic version, pixi
builds the package metadata to lock, which needs the conda environment
installed. Run `pixi lock` and commit the result before pushing; the site
workflow installs with --locked.

pixi run check passes; no computed value, vector, fixture, schema or SQL
file changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/oracle/fingerprint.py

@@ -1,66 +0,0 @@
-"""Page fingerprints, scienting-page/1, and download-stamp rules, scienting-stamps/1.
-
-Non-normative; see spec/07-geometry.md.
-"""
-
-import math
-import re
-import unicodedata
-
-from . import jcs
-from .notation import fold_plain_text
-from .text import is_ws, norm, sha256_hex
-
-
-def round_point(x):
-    """Round half up to a whole point."""
-    return int(math.floor(x + 0.5))
-
-
-def _in_margin(box, size, margin):
-    x0, y0, x1, y1 = box
-    w, h = size
-    return x1 <= margin or x0 >= w - margin or y1 <= margin or y0 >= h - margin
-
-
-def is_stamp(line, size, rules):
-    text = norm(line["text"])
-    for r in rules:
-        if r.get("where", "any") == "margin":
-            if "box" not in line or not _in_margin(line["box"], size, r.get("margin", 36)):
-                continue
-        if re.search(r["pattern"], text, re.IGNORECASE | re.ASCII):
-            return r["id"]
-    return None
-
-
-def _strip(s):
-    return "".join(c for c in s if not is_ws(c) and unicodedata.category(c) not in ("Cc", "Cf"))
-
-
-def fp_text(text):
-    """Steps 3 and 4 of spec/07 §7.1: whitespace and control characters go first, so that "10 -20" and "10-20"
-    fold alike; then scripts and dashes fold as in the strict projection, then NFKC."""
-    return _strip(unicodedata.normalize("NFKC", fold_plain_text(_strip(text))))
-
-
-def fingerprint(page, rules):
-    """`page`: {"size": [w, h], "lines": [{"text", "box"?}], "images": [sha256...]}.
-
-    Returns (fingerprint, removed stamp rule IDs in line order).
-    """
-    size = page["size"]
-    kept, removed = [], []
-    for line in page.get("lines", []):
-        rid = is_stamp(line, size, rules)
-        if rid:
-            removed.append(rid)
-        else:
-            kept.append(line["text"])
-    payload = {
-        "format": "scienting-page/1",
-        "size": [round_point(size[0]), round_point(size[1])],
-        "text": fp_text(" ".join(kept)),
-        "images": sorted(page.get("images", [])),
-    }
-    return sha256_hex(jcs.dumpb(payload)), removed