Scaffold CMOS 18 reformatter: harness, linter, parser, formatter, CLI

Initial phase-1 baseline of the karpathy/autoresearch-style loop.
The formatter module is the inner-loop artifact; parser and linter
are infra. The linter carries a LINTER_VERSION hash (v0.2.0) that
will force a re-baseline on any rule change.

Components:
- harness/diff.py: case-sensitive field-level substring diff
- harness/score.py: three-axis scoring (field, linter, canary exact)
- src/cmos/linter.py: 9 CMOS 18 structural rules, each Purdue/CMOS cited
- src/cmos/parser.py: locate ## Bibliography section, split entries
- src/cmos/formatter.py: prompt + OpenAI call with caller injection
- src/cmos/cli.py: cmos format path/to/draft.md
- scripts/run_loop.py: loop runner with --fake mode for no-API runs
- exemplars/: 3 canary seed exemplars (book, journal w/DOI, web),
  sourced from chicagomanualofstyle.org quick guide

Tests: 48 passing. Fake-mode baseline scalar = 0.000 on the 3 seed
exemplars (identity caller fails the linter on every rule). This is
the floor the real GPT-5 formatter needs to improve from.

exemplars/web_page_google_privacy.toml

@@ -0,0 +1,16 @@
+# Source: CMOS official citation guide (chicagomanualofstyle.org), 18th ed.
+# Demonstrates: web page with "Effective" date (rather than access date).
+# Site owner / corporate author sits in the author slot when no personal author exists.
+source = "CMOS official citation guide (chicagomanualofstyle.org/tools_citationguide/citation-guide-1.html)"
+type = "web"
+tags = ["web", "corporate-author"]
+canary = true
+messy_input = "google, \"privacy policy,\" privacy & terms, effective nov 15 2023, policies.google.com/privacy"
+expected_bibliography = "Google. \"Privacy Policy.\" Privacy & Terms. Effective November 15, 2023. https://policies.google.com/privacy."
+
+[canonical]
+author = "Google"
+title = "Privacy Policy"
+site = "Privacy & Terms"
+date = "November 15, 2023"
+url = "https://policies.google.com/privacy"