Move docs/ package mirror into document-navigator plugin

Relocate the ~6k-file docs tree from the repo root into
plugins/document-navigator/docs/ so the plugin is self-contained and
portable. docs/superpowers/ (specs and plans) stays at the repo root.

Moved via cp+rm rather than git mv because directory rename() fails with
EPERM on this WSL /mnt DrvFs mount; git rename-detection pairs the
identical-content files at commit time.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/document-navigator/docs/media/image/emblem-solver/src/helpers/helpers.md

@@ -0,0 +1,85 @@
+# `helpers/helpers.ts` — packing, keys, and grid primitives
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+This module is the shared kernel of utility functions used by the analyser,
+the solver strategies, and the optimisers. It owns the canonical
+representation of a pixel index (a packed `y * width + x` integer), the
+canonical colour key (`"r,g,b"`), the `computeBounds` reduction over a
+packed-pixel set, and the boolean-grid builders that drive the
+maximal-rectangle sweep and per-layer covering.
+
+## Features
+
+- `pack` / `unpackX` / `unpackY` give the package a single, branch-free way
+  to convert between `(x, y)` and a single integer. Using a `Set<number>`
+  of packed indices is dramatically cheaper than a `Set<string>` of
+  `"x,y"`.
+- `colourKey` / `parseKey` round-trip an RGBA without committing to alpha;
+  the solver does not need alpha for keying.
+- `computeBounds` is the only place we touch unpack-loop machinery for
+  bounds computation; everywhere else delegates here.
+- `isFullyAvailable`, `rectCoversAnyRequired`, and `countRequired` are the
+  three predicates the optimiser relies on; they share an early-exit
+  pattern that keeps the solver O(area × candidates) rather than
+  O(area² × candidates).
+- `buildAvailableGrid` / `buildRequiredGrid` allocate the 2-D `boolean[][]`
+  masks used by the cover strategies.
+
+## Usage: Basic
+
+```ts
+import { pack, unpackX, unpackY } from "@suaveplan/emblem-solver";
+
+const w = 8;
+const idx = pack(3, 2, w); // 19
+unpackX(idx, w); // 3
+unpackY(idx, w); // 2
+```
+
+## Usage: Advanced
+
+```ts
+import {
+    buildAvailableGrid,
+    buildRequiredGrid,
+    isFullyAvailable,
+} from "@suaveplan/emblem-solver";
+
+const opaque = new Set<number>([0, 1, 2, 3]);
+const earlier = new Set<number>();
+const avail = buildAvailableGrid(2, 2, opaque, earlier);
+const req = buildRequiredGrid(opaque, 2, 2);
+isFullyAvailable({ x: 0, y: 0, w: 2, h: 2 }, avail); // true
+```
+
+## API Reference
+
+| Symbol | Kind | Description |
+|---|---|---|
+| `pack(x, y, w)` | fn | Row-major packed index |
+| `unpackX(i, w)` | fn | Recover `x` |
+| `unpackY(i, w)` | fn | Recover `y` |
+| `colourKey(rgba)` | fn | `"r,g,b"` |
+| `parseKey(str)` | fn | `RGBA` with `a:1` |
+| `computeBounds(set, w)` | fn | Tight bounding `Rect` |
+| `isFullyAvailable(rect, grid)` | fn | All cells `true`? |
+| `rectCoversAnyRequired(rect, req)` | fn | Any overlap? |
+| `countRequired(rect, req)` | fn | Overlap count |
+| `buildAvailableGrid(w, h, opaque, earlier)` | fn | 2-D opaque mask minus earlier layers |
+| `buildRequiredGrid(set, w, h)` | fn | 2-D mask from packed pixel set |
+
+## Implementation Notes
+
+The functions are deliberately monomorphic over `boolean[][]`/`number` for
+predictable JIT performance. The bounding-box reduction uses `±Infinity`
+sentinels so it works for any non-empty set. The available-grid builder
+skips earlier-layer pixels in O(1) per packed index — important when the
+solver iterates orderings exhaustively over a colour set. None of these
+helpers allocate beyond the grids they explicitly build; the predicates
+return as soon as their early-exit condition is met, so worst-case work is
+bounded by `rect.w * rect.h`.