Fix fresh sync failure at diff reset height 2838976

Fresh-syncing nodes rejected the on-chain min-diff block at the
RANDOMX_VALIDATION activation height (2838976) because GetNextWorkRequired
computed the expected nBits from the preceding normal-difficulty blocks,
producing 469847994 instead of the on-chain 0x200f0f0f (HUSH_MINDIFF_NBITS).
This caused all seed nodes to be banned with "Incorrect diffbits" and the
node could never sync past that height.

Two changes:

1. GetNextWorkRequired (pow.cpp): Return nProofOfWorkLimit at the exact
   RANDOMX_VALIDATION activation height, matching the on-chain diff reset.

2. ContextualCheckBlockHeader (main.cpp): Raise DragonX daaForkHeight to
   RANDOMX_VALIDATION + 62000, covering the window where nBits was never
   validated (diff reset at 2838976 through the attack at ~2879907).

Tested by invalidating block 2838975 and reconsidering — node re-validated
through the diff reset and attack window, syncing back to tip with zero
bad-diffbits rejections.

Bump version to 1.0.1.

src/clientversion.h

@@ -30,7 +30,7 @@
 // Must be kept in sync with configure.ac , ugh!
 #define CLIENT_VERSION_MAJOR 1
 #define CLIENT_VERSION_MINOR 0
-#define CLIENT_VERSION_REVISION 0
+#define CLIENT_VERSION_REVISION 1
 #define CLIENT_VERSION_BUILD 50
 
 //! Set to true for release, false for prerelease or test build