Reorganize docs into category folders and drop the retired head-review page

Group the top-level docs into docs/project, docs/design, docs/assets and
docs/process, each with its own README index. Delete the superseded
docs/screens/head-review page and sheets. Rewrite every markdown link,
absolute docs path and tool/test reference to the new locations, fix the
pre-existing broken anchors and remove the dead Joke Shop photo-board link.
check_docs OK, Python tooling 167/167.

docs/design/accessibility.md

@@ -0,0 +1,32 @@
+# Accessibility Statement
+
+Gig Line is a keyboard/mouse-first first-person game with gamepad support. The
+current build includes the following accessibility features:
+
+- Remappable keyboard and gamepad bindings, persisted in `settings.json`.
+- Keyboard focus rings and explicit default focus in every modal, with A/B
+  accept/cancel on a gamepad and wrapped Tab/arrow navigation.
+- Adjustable HUD font scale up to 1.75× with clipped/ellipsized long labels.
+- Reduced-motion mode that disables head bob and motion-sensitive presentation.
+- Captions in the HUD log for radio, interaction and event messages.
+- Master, SFX and ambience volume controls.
+- Shape plus number escalation meter, so escalation is readable without colour.
+- Hold-to-confirm emergency action and guarded destructive actions.
+- Searchable Help generated from the live input bindings.
+- Mouse-transparent HUD, right-click/Esc modal handling, and a predictable
+  top-panel close path.
+
+Known gaps:
+
+- There is no screen-reader integration or text-to-speech narration.
+- The game is English-only; no pseudo-locale or full localization review has
+  been completed.
+- The visual style is stylized and some small environmental detail may be hard
+  to read at low resolution; a full low-vision/high-contrast audit is pending.
+- Audio captions cover gameplay messages, not every ambient sound.
+- A formal WCAG conformance claim has **not** been made. External accessibility
+  review is still a 0.10.0 release-review item.
+
+Test evidence and the manual checklist live in
+[`release-qa.md`](../process/release-qa.md#manual-smoke-checklist); settings and save behaviour are
+documented in [`getting-started.md`](../process/getting-started.md).