feat(campaigns): separate GM truth from PC knowledge

Hidden truth lives in gm/; state/knowledge.md holds what the PC knows,
believes, and suspects. Everything else in a campaign stays player-facing.

campaigns/_template/state/knowledge.md

@@ -0,0 +1,31 @@
+# What the PC knows
+
+The PC's working picture of the world — not the world itself. Narration may draw
+on these entries and on what the PC perceives now; anything the PC has not
+learned belongs in `../gm/`.
+
+Update this file whenever a scene reveals something, confirms a suspicion, or
+overturns a belief. A mistaken belief stays here under Suspected until the PC
+learns better, even after the GM knows the truth.
+
+## Known
+
+Facts the PC has learned or observed, and where they learned them.
+
+| Fact | Learned |
+|------|---------|
+|      |         |
+
+## Suspected
+
+Things the PC believes but has not confirmed — including beliefs that are wrong.
+
+| Belief | Basis |
+|--------|-------|
+|        |       |
+
+## Open questions
+
+Questions the PC is actively trying to answer.
+
+-