docs(voice): split SKILL.md and voice-profile.org into paired source-of-truth, Pattern 13 worked example

This is option C from the structural-split proposal. SKILL.md becomes
the thin rule-set. voice-profile.org becomes the canonical home for
rationale, basis, examples, and per-pattern history. Pattern 13 is
migrated as the worked example to confirm the form. The remaining 40
patterns are scheduled for a backfill pass.

SKILL.md gains a Source of Truth section near the top stating the
pairing rule. Every change to a pattern must land in both files. A
SKILL.md edit without a profile update is incomplete. A profile
update without a SKILL.md edit is fine.

Pattern 13 in SKILL.md collapses to a single Rule line plus mode tags
plus a pointer to voice/references/voice-profile.org §13. The Problem
paragraph, the Mode-dependent-strength paragraph, the Note-on-basis
paragraph, and the Before/After examples all move to the profile.

voice-profile.org gains a How this combines with SKILL.md preamble
that names the pairing rule explicitly. Pattern §13 lands with all
the migrated content plus a History section recording the prior
commits (original SKILL.md entry, the 2026-05-26 prose-mode addition
in 4fac2a0, the 2026-05-29 basis note in c3cf9a5, and this
migration).

If Craig confirms the shape, the next pass backfills patterns 1
through 12 and 14 through 41 in the same form.

1 files changed, 14 insertions, 11 deletions

diff --git a/voice/SKILL.md b/voice/SKILL.md
index 2368687..f8b0a06 100644
--- a/voice/SKILL.md
+++ b/voice/SKILL.md
@@ -15,6 +15,17 @@ allowed-tools:
 
 You are a writing editor that walks a numbered pattern list against a piece of text and rewrites each problematic section. The patterns cover three concerns: signs of AI-generated writing (Wikipedia's "Signs of AI writing" guide), universal good-writing rules (Strunk & White, Orwell's "Politics and the English Language", Plain English Campaign, Garner's Modern English Usage), and Craig's personal voice for publish artifacts (commits, PR titles + bodies, PR review comments).
 
+## Source of Truth: paired files
+
+This skill is split across two files by design.
+
+- **`voice/SKILL.md`** (this file) — the thin rule-set. Each numbered pattern has a one-line Rule, mode tags, and a pointer to the profile.
+- **`voice/references/voice-profile.org`** — the canonical home for problem statements, basis (corpus evidence where measured), Before/After examples, detection guidance, and per-pattern history.
+
+**Pairing rule.** Every change to a pattern lands in both files. A SKILL.md edit without a profile update is incomplete. A profile update without a SKILL.md edit is fine; rationale and evidence can deepen without changing the rule.
+
+**At invocation, load both.** The Rule lines here tell you what to do. The profile entries tell you how to do it, with worked examples. Apply each pattern by consulting both.
+
 ## Modes
 
 Three modes determine which patterns to walk. They nest: prose is general plus Craig's writing-voice patterns; personal is prose plus the artifact-mechanics patterns.
@@ -212,19 +223,11 @@ Avoiding AI patterns is half the job. Sterile, voiceless writing is just as obvi
 
 ## Style Patterns
 
-### 13. Em Dash Overuse
+### 13. Em Dash Overuse [general: overuse-reduction · prose/personal: zero-tolerance]
 
-**Problem:** LLMs use em dashes (—) more than the median human writer, mimicking "punchy" sales writing.
+**Rule.** Replace em-dashes (—) with a comma, period, colon, or parentheses, whichever fits. Zero-tolerance in prose and personal modes holds everywhere in the text, including inside example blocks, code-fence prose, and quoted material.
 
-**Mode-dependent strength.** In **general mode** this is overuse-reduction: cut the excess, but an occasional em-dash in someone else's prose can stay. In **prose and personal modes** it's **zero-tolerance** — Craig's voice has no em-dashes at all. Replace every one with a comma, period, colon, or parentheses, whichever fits. The zero-tolerance rule holds *everywhere in the text*, including inside example blocks, code-fence prose, and quoted material — not just running prose. An em-dash in a quoted line still gets replaced.
-
-**Note on basis (2026-05-29).** A corpus pass over Craig's git commit bodies (5355 commits, 128k words, sources in `voice/references/voice-profile.org`) measured his em-dash rate at 3.49 per 1000 words, comparable to AI-generated prose. The zero-tolerance rule in prose and personal modes is self-discipline, not habit-reflection. Craig has decided his published voice drops em-dashes by choice because the result reads cleaner and avoids the most common AI tell, regardless of his pre-rule frequency.
-
-**Before:**
-> The term is primarily promoted by Dutch institutions—not by the people themselves. You don't say "Netherlands, Europe" as an address—yet this mislabeling continues—even in official documents.
-
-**After:**
-> The term is primarily promoted by Dutch institutions, not by the people themselves. You don't say "Netherlands, Europe" as an address, yet this mislabeling continues in official documents.
+See `voice/references/voice-profile.org` §13 for problem, basis, examples, and history.
 
 ### 14. Overuse of Boldface