docs: land the saga guardrails on the milestones they constrain

Applies the seven-campaign saga direction spec (021c248) to the docs it
was written to protect. No new milestone, no new content, no BOM line.

docs/roadmap.md — a "Guarded direction" section, and a ⛨ saga note on the
four milestones that would otherwise foreclose the shape:
  M3  don't hardcode the title flow so a saga entry path can't be added
  M4  keep construct()'s `creation` a plain Dictionary; the scene must not
      become its only producer
  M5  the level curve is no longer open — L20 across 7 tiers; enemy stat
      blocks carry tier; no scaling multiplier, ever
  M9  the save is two objects (Saga + Campaign); humiliations move to the
      Saga or they die with the campaign

races-and-classes spec — the deferred "XP curve → M5" line now inherits the
ceiling rather than choosing one.

canon-roadmap — what the saga asks of content: a tier field when the
item/quest namespaces land, and a fixed-vs-variable mark on each BOM line
when the BOM is written. Tiers 2-7 and the other six kings go to the
Backlog.

Content build --check green; no generated content touched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-07-11-races-and-classes-design.md

@@ -209,6 +209,10 @@ Nothing here silently pre-empts a later brainstorm.
 - The **damage-determinism reconcile** (§7/§10 vs the Combat HUD mock's ranges).
 - The **borderline band size** (DC bands).
 - Leveling — hit-die progression, prof-bonus scaling, talent tiers, XP curve. (Creation is L1.)
+  **The ceiling is no longer open:** the seven-campaign saga
+  ([spec](2026-07-12-character-reuse-seven-arc-design.md)) fixes it at **L20 across 7
+  tiers** (tier N ≈ levels 3N−2 … 3N). M5 designs the curve *to* that ceiling; it does
+  not choose it. An open-ended curve is unsolvable and forecloses the saga.
 
 **→ Canon session (lore):**
 - The two **[CANON-TBD]** calling names (Barbarian ⚔ / Warlock 🔥).