Tighten RSBK package-format validation for review remediation

Reject NUL/control bytes and Windows-hostile names in entry names, relax
the over-broad ".." substring ban to component-only, close the
trailing-garbage gap on empty manifests, and relocate the package
CMake subdirectory to its ladder home.

src/core/package/CLAUDE.md

@@ -26,9 +26,12 @@ landing after the format.
   else — no manifest, no layout, no half-success. The fields through the writer
   semver are FROZEN for all future versions to keep that refusal producible.
 - **Path expression is structurally impossible.** Entry names are bare file
-  names (`isValidEntryName`: no separators, no `..`, no drive/UNC/rooted form),
-  enforced on encode AND decode because a package can arrive from anywhere.
-  There is no field in the format capable of expressing a path.
+  names (`isValidEntryName`: no separators, no `..` component, no
+  drive/UNC/rooted form, no control bytes, no Windows-reserved character, no
+  trailing dot/space, no DOS device name), enforced on encode AND decode
+  because a package can arrive from anywhere. There is no field in the format
+  capable of expressing a path. The rule set is the full authority; see
+  `package_format.h`'s doc comment for the itemized list.
 - **Framing only, never a payload.** `bank_package` produces header bytes and
   an ordered `{name, offset, length}` layout; it never holds, copies, or hashes
   an entry's audio. `decodePackage` proves prefix + payload lengths equal the
@@ -76,3 +79,8 @@ landing after the format.
   version pair classifies `Readable`; for `TooNew` it stops at the semver —
   don't "fix" it to read the manifest length there, a future structural format
   may have moved it.
+- The format carries no algorithm tag for `byteHash` — it is FNV-1a
+  (`capture::hashBytes`) implicitly. Changing the digest algorithm is a
+  `minReaderVersion` bump, not additive: an old reader would otherwise compare
+  a stored digest against bytes hashed the new way and silently misjudge
+  corruption.