Prepare 0.9.6-SNAPSHOT with DH input validation and distinct signer checks

SECURITY-0.9.5.md

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+# crypto2 0.9.5 security fix
+
+`Multikey.Keys.check` now counts distinct authorized signer keys. Earlier versions
+could count repeated copies of one allowed key toward an N-of-M threshold.
+A serialized `SealedBox` containing repeated copies of a valid seal could therefore
+pass threshold authorization without the required distinct signers. Signature
+verification itself was not forged. Policies built with `someOf` or `allOf`,
+including these thresholds inside nested expressions, were affected.
+
+Upgrade consumers to 0.9.5. Wire formats and public APIs are unchanged. Repeated
+seals remain readable but cannot supply extra votes. Boolean expression semantics
+(including intentionally overlapping branches) are unchanged.
+
+Regression coverage includes exhaustive subsets for one through four required
+keys, duplicate and unauthorized signers, nested policies, and serialized seal
+repetition with valid distinct-signature controls.
+
+Release qualification: all 64 JVM tests and all 64 Linux x64 native tests pass.
+The JavaScript/Node suite cannot complete: 61 of 64 tests fail at the existing
+libsodium loader (`_sodium_init is not a function`). An unchanged-source signing
+test reproduces that same failure; this release does not fix the JS loader.
+All 12 configured publications were uploaded to Maven Local and the private Maven
+repository; SHA-256 comparison of 53 downloaded release files matched Maven Local.