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/foundation/bitpacker/bitpacker-delta/src/string-diff.md

@@ -0,0 +1,26 @@
+## String Diff
+
+**Path:** `src/string-diff.ts`  
+**Export:** `calculateStringDiff`, `applyStringDiff`, `calculateDiffSavings`, `shouldUseDiff`, `StringDiff`
+
+### What it does
+
+Efficiently encodes string changes by finding common prefix and suffix, only encoding the differing middle section.
+
+### Key API
+
+| Function | Description |
+|----------|-------------|
+| `calculateStringDiff(previous, current)` | Compute `{ prefixLen, suffixLen, middleLen, middle }` |
+| `applyStringDiff(previous, diff)` | Reconstruct current string from diff |
+| `calculateDiffSavings(previous, current, diff)` | Percentage savings from diff encoding |
+| `shouldUseDiff(previous, current, threshold?)` | Decide whether diff encoding is worthwhile |
+
+### Format
+
+`[prefixLen][suffixLen][middleLen][middleChars...]` — each length field is 1 byte.
+
+### Used by
+
+- Delta compression for string fields in game state
+- Network protocols with repetitive string data