docs(arch): realism leads the quality list; performance moves to the end

Owner decision: prioritise realism, keep the performance target but put it last.
Re-applied on a branch after the first attempt landed directly on main (reverted
there; see b8209ce).

- Quality goals (01 + combined architecture.md): 1 visual realism, 2 geographic
  fidelity, 3 walkability/usability, 4 reproducibility/portability, 5 provenance,
  6 performance efficiency.
- Quality requirements (10 + combined) reordered to match, with two realism
  requirements added (a façade reads like the photographs; placement within ~1 m)
  and the scenarios renumbered so QS-1 is the reference comparison, QS-9 the frame
  rate.
- Guard on both documents so the order cannot become an excuse: performance is a
  floor, not a preference - 60 FPS at 1440p without frame generation must be met at
  every release; if realism cannot fit, cut the realism scope deliberately and
  record it, never the frame rate. Walkability outranks realism in one direction: a
  block you fall through is not a demo.
- Solution strategy and 'quality achievement' lead with realism and describe
  performance as a budget, not a driver.
- Docs/release-checks.md: the performance check is the last section and the per-
  version check list now opens with realism and closes with performance.
- ROADMAP gains a 'Quality priority' section; AGENTS.md gains the tie-break rule
  beside the existing scope-cutting rule.

AGENTS.md

@@ -67,6 +67,7 @@ Rules for `TODO.md`:
 - When **all** steps in a version section are done: write a short descriptive entry to `CHANGELOG.md`, remove the version section from `TODO.md`, and leave its goal in `ROADMAP.md`.
 - Release checks for each version are listed at the end of its `TODO.md` section; `Docs/release-checks.md` defines the checks themselves. If a check fails, do not tag the release; open a patch task in `TODO.md` and report the failing check in `CHANGELOG.md`.
 - Finish each milestone's release checks **before** expanding scope. Cut map size and simulation complexity before compromising the core walking/driving experience.
+- **Realism leads, performance is a floor.** When a realism improvement costs frame time, realism wins and the cost is paid — but 60 FPS at 1440p without frame generation must still be met at every release. If realism cannot fit the budget, reduce the realism scope deliberately and record it in `CHANGELOG.md`; never ship below the floor without the owner's approval. Walkability outranks realism in one direction only: a block the player falls through is not a demo.
 
 ## Git workflow