Merge plan for Codex's stack after Codex stopped #161

Problem

Codex's stack is 16 open layers (#111 → #149) plus our layer 17 on top (#155) and #154 on main. None of it is on main, so production still has no movement. Codex has stopped, so the stack needs one plan: what merges as is, what gets reworked, and in which order, so the slice is playable before the 11:00 freeze.

Plan

flowchart LR
  S["#111 … #149<br/>Codex stack<br/>(green, MERGEABLE)"] --> M1["merge bottom-up<br/>on Alexander's word<br/>(merge-async on the top)"]
  P155["#155 [17] region route"] --> M1
  M1 --> MAIN["main"]
  P154["#154 coffee visit"] --> MAIN
  MAIN --> F["rework on top:<br/>feel, timing from anims.json,<br/>data not hardcode"]

Acceptance criteria

• Decision recorded in docs/11: merge the stack as the base, then rework on top, never a rewrite.
• Merged: the stack is on main, bottom-up, after every layer's checks pass and Alexander says go.
• Synced: feat: seat Dexter at the coffee machine with his gifts #154 and [17/20] feat: swap regions on the route to the maze #155 are synced after the merge.
• Issues closed: every lane B issue the stack closes is closed or retargeted.