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-crypto/src/xxhash32.md

@@ -0,0 +1,31 @@
+## xxhash32
+
+**Path:** `src/xxhash32.ts`  
+**Export:** `calculateXxhash32`, `verifyXxhash32`, `packXxhash32`, `unpackXxhash32`, `appendXxhash32`, `verifyAndStripXxhash32`
+
+### What it does
+
+Pure TypeScript implementation of the XXHash32 non-cryptographic hash algorithm (spec v0.8.2). No external dependencies.
+
+### Key API
+
+| Function | Description |
+|----------|-------------|
+| `calculateXxhash32(data, seed?)` | Compute 32-bit hash of a `Uint8Array` |
+| `verifyXxhash32(data, expected, seed?)` | Verify a hash matches |
+| `packXxhash32(checksum)` | Pack hash as 4 little-endian bytes |
+| `unpackXxhash32(bytes, offset?)` | Unpack 4 bytes to hash value |
+| `appendXxhash32(data, seed?)` | Append 4-byte hash to data |
+| `verifyAndStripXxhash32(data, seed?)` | Verify and strip appended hash |
+
+### Constants
+
+- `PRIME1` = `0x9e3779b1`
+- `PRIME2` = `0x85ebca77`
+- `PRIME3` = `0xc2b2ae3d`
+- `PRIME4` = `0x27d4eb2f`
+- `PRIME5` = `0x165667b1`
+
+### Used by
+
+- Checksum validation in downstream network protocols