feat(preamble): T3 — jargon dedup + terse-build flag (Phase A.2 + A.3)

A.2 jargon dedup: generate-writing-style.ts replaces the inlined 80-term
jargon list with a one-line pointer to scripts/jargon-list.json. The list
was duplicated into every tier-2+ skill (48 of 51 skills); inlining cost
was ~1.5 KB × 48 = ~70 KB across the corpus. Pointer cost is ~30 bytes per
skill. Agents Read the JSON once per session on first jargon term
encountered; thereafter the terms array is the canonical reference.

A.3 terse build flag: --explain-level=terse compresses preamble prose at
gen time. When the flag is set, writing-style collapses to a one-line
terse directive and completeness-section + confusion-protocol +
context-health are dropped entirely. The default build keeps the
runtime-conditional behavior intact (sections still render; the model
skips them when EXPLAIN_LEVEL: terse appears in the preamble echo). Terse
build is opt-in for users who want shipped skills to match their runtime
preference and avoid the per-session terse-mode dead prose.

TemplateContext gains an optional `explainLevel: 'default' | 'terse'`
field. Default builds set it to 'default'; --explain-level=terse sets
'terse'. Resolvers gate their output via `ctx?.explainLevel === 'terse'`.

Measured impact (default build, post-T3):
- Total corpus: 2,847 KB → 2,812 KB (saved 35 KB)
- ship.md: 160 → 159 KB
- plan-ceo-review.md: 128 → 127 KB
- Top 10 heaviest: all slightly smaller from jargon pointer

Larger compression lands in T4 (catalog trim) and T7 (atomic regen across
the full Phase A pipeline). The terse build path further compresses to
~711K tokens vs default ~725K (saved ~14K tokens corpus-wide).

Test plan:
- bun test test/gen-skill-docs.test.ts: 389 pass (no regression)
- bun test test/resolver-entry.test.ts: 6 pass
- bun test test/helpers/capture-parity-baseline.test.ts: 4 pass
- bun run gen:skill-docs --explain-level=terse: ship.md drops completeness +
  confusion-protocol + context-health sections; writing-style collapses to
  one-line terse directive

48 SKILL.md files updated (every tier-2+ skill picks up the jargon pointer).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/resolvers/types.ts

@@ -62,6 +62,22 @@ export interface TemplateContext {
   preambleTier?: number;  // 1-4, controls which preamble sections are included
   model?: Model;  // model family for behavioral overlay. Omitted/undefined → no overlay.
   interactive?: boolean;  // true → emit plan-mode handshake in preamble. Generator-only, not written to SKILL.md.
+  /**
+   * Build-time compression mode. Defaults to 'default'.
+   *
+   * - 'default': full preamble prose ships as today (writing style, completeness,
+   *   confusion protocol, context health are all present).
+   * - 'terse': writing-style + completeness + confusion-protocol + context-health
+   *   sections are compressed to a one-line pointer at gen time. Saves ~3-5 KB
+   *   per tier-2+ skill. Opt-in via `--explain-level=terse` build flag for
+   *   users who want shipped skills to match their runtime preference and
+   *   avoid the per-session terse-mode prose.
+   *
+   * Default builds keep the runtime-conditional behavior intact (Writing Style
+   * section says "skip entirely if EXPLAIN_LEVEL: terse appears in preamble echo").
+   * Terse builds make the compression structural — bytes never ship in the first place.
+   */
+  explainLevel?: 'default' | 'terse';
 }
 
 /** Resolver function signature. args is populated for parameterized placeholders like {{INVOKE_SKILL:name}}. */