docs(skill): fan-out token-economy guidance + track nomarchy skill

Add a "Fanning out worktree agents" subsection to §6.5: match model to
task (sonnet for spec'd work, opus for judgment), point briefs at the
backlog spec, disjoint file lanes, worktree isolation with the parent
owning landing, lean on scriptable checks as evidence, batch V2 in one
VM pass. First commit of the tracked skill (skills were un-ignored in
7d52d4b). MEMORY note updated: skills are now tracked.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/MEMORY.md

@@ -110,7 +110,8 @@ iteration would otherwise rediscover.
   effects carry a value, matchers take `match:` (§ windowrule migration).
 - grub `loadfont`s every `.pf2` in a theme dir — reuse a bundled DejaVu
   rather than shipping fonts (§ Distro branding).
-- The Claude Code harness drops machine-local files into the repo
-  (`.claude/skills/…`) mid-session — never `git add -A` blindly; check
-  `git status --short` for strangers first (they're gitignored now, but
-  the next surprise won't be) (§ loop hygiene).
+- `.claude/skills/*/SKILL.md` are now **tracked** (the `.gitignore`
+  `.claude/skills/` line was un-commented→removed, 7d52d4b) — commit skill
+  edits like any repo doc. Still never `git add -A` blindly: check
+  `git status --short` for genuine strangers first (`settings.local.json`,
+  harness-dropped files) and commit with explicit pathspecs (§ loop hygiene).