docs(p3-29): cite iter_7m proof scene authoring in render bullet (scene verified, PNG pending fleet)

- Added file:line + commit 31977522 cite for the new scene (prepares phase gate).
- Render proof acceptance remains open (no reviewed PNG yet; K<N).
- Per objective-integrity: status stays partial until full K==N with screenshot evidence.

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

.project/objectives/p3-29-rail1-turn-unification.md

@@ -170,6 +170,10 @@ healed besieged cities → siege-suppress (de68c9c10). All headless prep for the
   `RUST_FAUNA_ENCOUNTERS` flag, not the whole-round `RUST_TURN` path — a NEW proof scene is needed
   that drives `end_turn()` through a full round with `RUST_TURN=1` and shows state advancing +
   rendering. DO `dist:render` (software weston/Mesa) is the available render host (apricot/plum).
+  Scene authored + verified parse/exec (local godot --headless RUST_TURN=1 reached drive + capture):
+  src/game/engine/scenes/tests/iter_7m_rust_turn_full_round_gated_proof.{gd,tscn} (31977522);
+  follows godot-engine conventions, 7k/7p patterns, self-captures, preloads, uses TurnManager.end_turn
+  at round boundary. PNG review + contract labels pending fleet host resolution (token + tier size).
 - [ ] GUT green; headless `mc-turn` already proven (it IS the step being adopted). Pre-commit
   check: the flagged change loads clean headless (no parse/script errors, autoload registers).