feat(skills): add project-local world-building skill

Author gritty, disposition-gated Margreave content (lore bible + hand-authored
quest/item/location/origin JSON) that reconciles against existing canon before
writing, holds the world's hard-by-default / warm-when-earned NPC tone, and keeps
the content_build --check gate green.

- SKILL.md: read-before-write workflow, read-only on existing canon (propose
  diffs, require approval), build+check+pytest as the done bar.
- references/schema.md: full bible + JSON contract, secrecy scale, gate model.
- references/tone.md: tone contract + NPC disposition-warmth model.
- scripts/canon_index.py: dumps existing ids for reconciliation.
- evals/: 3 test cases (all green in isolated-worktree runs).

Un-ignore /.claude/skills/ so project skills are versioned like code; all other
.claude/ dirs (root + nested api/client) stay ignored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HuHRPE7VfppUJEaoGBEUqZ

.claude/skills/world-building/references/tone.md

@@ -0,0 +1,104 @@
+# Tone — the Margreave
+
+The world's voice. Distilled from charter §3 (tone), §7 (Luck), §9 (companions).
+Read before writing any `body`, persona, or narrative prose. Getting this right is
+most of the job — the schema is easy; the voice is the product.
+
+## The core stance
+
+**Gritty, not grim.** The reference is Batman in the DC comics — not Warhammer,
+not Care Bears. The world has real problems and does not care about the player.
+People get hangovers, vomit, curse, get infected wounds. But it is not a misery
+engine. Grimdark is as wrong as cozy. The world is *indifferent*, and indifference
+is harder and more interesting than cruelty.
+
+**The world is played straight.** Comedy emerges from situation, never from the
+narrator. Nothing is ever "hilariously" anything. The narrator is dry and does not
+wink. When you're tempted to make prose funny, make the *situation* absurd and
+describe it flatly instead.
+
+## Register
+
+- **Profanity** is permitted and should feel *earned*, not decorative.
+- **Violence has weight.** Don't gloss it and don't wallow.
+- **Sex exists** and is discussed the way adults discuss it — bluntly, and mostly
+  as a source of trouble.
+- **Bodies are real.** Fatigue, hunger, cold, drink, injury. The world touches the
+  characters physically.
+
+## The narrator voice
+
+Dry. Economical. Observational. States what is, lets the reader feel the weight.
+It never editorializes, never reassures, never jokes. A good body reads like
+someone who has seen a lot and is not impressed, telling you the truth plainly.
+
+Look at the `duncarrow.md` bodies: "prosperous and orderly place, which is exactly
+the reputation its mayor has spent fifteen years building and depends on." The
+menace is in the plain statement, not in adjectives.
+
+## NPCs: hard by default, warm when earned
+
+This is the load-bearing pattern for the user's world. **The world doesn't care
+about you — but a person who comes to trust you does.** That arc is what the
+disposition ladder exists to deliver, and it's what makes the coldness bearable.
+
+### Default posture: guarded
+
+A Margreave NPC meets a stranger with wariness, not hostility — they have their
+own troubles and no reason to spend them on you. Mechanically:
+
+- `start_disposition` is usually `cold` or `neutral`, rarely `warm`.
+- A frightened or burned NPC withholds **more** than a stranger would expect, not
+  less (fear reads as prickliness — Mera Fenn is the model). `hostile` is a
+  reachable floor: push them, threaten, side against them, and they close entirely.
+- What they reveal is gated. Low rungs get you surface; the personal and the
+  dangerous sit higher up.
+
+### The warm turn: real, specific, earned
+
+When the player climbs the ladder, two things change together:
+
+1. **They reveal more** — deeper `knows` gates unlock.
+2. **Their manner softens** — write the persona and `disposition_notes` so that at
+   `warm`/`trusted` the dryness turns to something human: fondness, relief at being
+   heard, blunt loyalty. Old Teague's "dryness turns to something almost fond."
+
+The warmth is never sycophantic and never a personality transplant — a hard person
+stays recognizably themselves, just no longer guarded against *you*. That's more
+affecting than a switch from mean to nice.
+
+**Don't** write an NPC who is friendly from hello (breaks the world) or one who
+stays cold no matter what (makes the ladder pointless and the world hopeless). The
+range between those poles is the whole design.
+
+## The companions set the tone (charter §9)
+
+If you write companion content, hold these exactly — they carry the register:
+
+- **Cadwyn Vell (Bard, NPC-only):** genuinely talented, reflexively lies about
+  small things and truthfully about large ones, does not know he is the problem and
+  never becomes self-aware. Florid performing, clipped when scared. The source of
+  chaos.
+- **Brannoc Thane (Sellsword):** dry, warm, economical, twenty years past his
+  prime and at peace with it. Says devastating things in the tone of a man
+  discussing weather. Holds the humiliation log — the callback engine. Not a grump;
+  *fond* of you, which is what makes it land.
+- The pair dislike each other mildly and permanently, and neither will leave the
+  other. Cadwyn generates, Brannoc annotates. Don't add a third to the loop.
+
+## Luck's fingerprint (charter §7)
+
+If content touches Luck: it is **visible in prose, never in numbers.** Never state
+a Luck value; render a descriptor ("Fortune spits on you"). Bad luck costs
+**dignity, not progress** — embarrassment, inconvenience, property damage, social
+catastrophe, minor injury. Never quest failure, permanent loss, or death. A cursed
+item that grants power at a Luck cost (+STR / −LCK) is the most interesting kind of
+item — lean into that.
+
+## Quick self-check before you ship a body
+
+- Did the narrator stay dry and out of the joke?
+- Is the hardness *indifference*, not sadism?
+- Does the NPC start guarded, with a real warm turn available up the ladder?
+- Would profanity/violence/sex here feel earned, not decorative?
+- Does anything contradict an existing canon body? (If yes → reconcile, don't ship.)