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/journal_with_doi_kwon.toml

@@ -0,0 +1,19 @@
+# Source: CMOS official citation guide (chicagomanualofstyle.org), 18th ed.
+# Demonstrates: journal article with DOI, which CMOS 18 prefers over generic URL.
+# Page range uses en-dash (–), not hyphen (-).
+source = "CMOS official citation guide (chicagomanualofstyle.org/tools_citationguide/citation-guide-1.html)"
+type = "journal"
+tags = ["journal", "doi", "single-author"]
+canary = true
+messy_input = "Kwon, Hyeyoung. \"inclusion work: children of immigrants claiming membership in everyday life.\" American Journal of Sociology, Vol. 127, Issue 6, 2022, pp. 1818-1859. DOI: 10.1086/720277"
+expected_bibliography = "Kwon, Hyeyoung. \"Inclusion Work: Children of Immigrants Claiming Membership in Everyday Life.\" *American Journal of Sociology* 127, no. 6 (2022): 1818–59. https://doi.org/10.1086/720277."
+
+[canonical]
+author = "Kwon, Hyeyoung"
+article_title = "Inclusion Work: Children of Immigrants Claiming Membership in Everyday Life"
+journal = "American Journal of Sociology"
+volume = 127
+issue = 6
+year = 2022
+pages = "1818–59"
+doi = "https://doi.org/10.1086/720277"