Ship the 0.9.0 production-quality milestone

Add mixer/accessibility settings, caption/reduce-motion hooks, audio volume
clamping, a 24-NPC performance smoke and shortened coat/dress stride for hem
clipping. Record the explicit Godot 4.3-CI/4.7-local matrix and the 0.9
production scope. Headless 250/250, Python 94/94, 24-NPC budget smoke passes.

docs/architecture.md

@@ -37,7 +37,7 @@ This document follows the structure of the arc42 architecture documentation temp
 - **MINOR** — new venues, NPC archetypes, systems, or features that are backward compatible.
 - **PATCH** — bug fixes and small polish that do not change behavior.
 
-The single source of truth for the version is `config/version` in `project.godot` (currently `0.8.1`). Each release is tagged in git as `v<version>` (e.g. `v0.6.0`). The `0.x` series is pre-1.0, so MINOR bumps may introduce breaking changes while the prototype is still stabilizing. `tools/build_releases.sh` and `tools/publish_release.sh` read the version from `project.godot`, so bumping it there is the only required step before a release. The full bump checklist lives in [`RELEASING.md`](RELEASING.md).
+The single source of truth for the version is `config/version` in `project.godot` (currently `0.9.0`). Each release is tagged in git as `v<version>` (e.g. `v0.6.0`). The `0.x` series is pre-1.0, so MINOR bumps may introduce breaking changes while the prototype is still stabilizing. `tools/build_releases.sh` and `tools/publish_release.sh` read the version from `project.godot`, so bumping it there is the only required step before a release. The full bump checklist lives in [`RELEASING.md`](RELEASING.md).
 
 ## 3. Context and Scope
 
@@ -219,6 +219,7 @@ The release process is: bump the version, run the full test suite and `tools/che
 - **Asset provenance and AI usage:** AI-assisted images/concepts are development inputs only; validated outputs are committed, audited and loaded through the same runtime asset contracts. Generated content must not become an offline/CI dependency.
 - **Campaign and checkpoint state:** `Campaign` owns venue order/progression; settings, campaign, completed shift history and a versioned pause checkpoint are separate JSON documents. The checkpoint snapshots coordinator systems, scheduler RNG and NPC presentation/access state; it deliberately does not serialize the tutorial overlay or transient input state.
 - **Difficulty:** easy/normal/hard only scale spawn pacing, NPC compliance tolerance and report-credibility strictness; access/escalation rules and emergency rarity are invariant.
+- **Settings and accessibility:** volume/motion/caption settings persist through `settings.json`; Help is generated from the input-binding catalogue and the HUD log is the text caption surface. The supported engine matrix is explicit (CI/release 4.3, local 4.7.2) rather than an implicit version drift.
 - **Documentation ownership:** `PLAN.md` owns design intent; `docs/gameplay.md` owns playable mechanics; `docs/architecture.md` owns system boundaries, data flow, constraints and cross-cutting decisions; ADRs own decision history; `docs/development-status.md` owns the implemented/gap list; `TODO.md` owns the roadmap; `MEMORY.md` owns gotchas and open questions. Specialized docs link to these rather than becoming competing sources of truth.
 
 ## 9. Architecture Decisions