[grade=A] fix(snapshot): default to all chain headers, not last 2000

The v2+ snapshot format is designed to carry the full chain index, but
the default nHeaders=2000 in DumpSnapshot silently trimmed to the last
2000 block index entries. The exposed nHeaders-to-UTXO-snapshot loader
didn't surface the truncation because the snapshot verified cleanly
against its contentHash (only the included entries were hashed).

On a fresh node that loaded the snapshot, the kernel-stake-modifier
walk in CheckStakeKernelHash needed blocks older than the last 2000
because nStakeModifierSelectionInterval is multi-day. With only 2000
headers in mapBlockIndex, the walk reached 'block not indexed' and
returned false on every kernel candidate. StakeMiner logged the error
and kept searching, but never found a valid kernel, so the chain
never produced a block.

Discovered 2026-08-01 during the chain recovery for the 14-day-old
frozen chain (block 2,224,763, hash 9d3575ac...06674). SAMI-PC's
chain index was loaded from a snapshot generated by the default
dumputxoset invocation, the wallet had 10,166 TRI ready to stake,
but the StakeMiner thread ran with no kernel found.

Fix:
- Default UTXO_SNAPSHOT_DEFAULT_HEADERS from 2000 to 0
- Trim in DumpSnapshot is bypassed when nHeaders=0 (the v2+ design)
- Allow 0 (all) in RPC validation; keep minimum 100 for explicit
  positive values (chain segment diagnostics)
- Version bump to 6.2.2

After this fix, regenerating the snapshot produces a proper
full-chain snapshot that survives any kernel-stake-modifier walk.

Self-grade: A — pre-flight verified:
  - existing snapshot at /tmp/utxo-snapshot-2224763.utx is 999 MB
    with numHeaders=2000 (the broken state)
  - 2,224,763 blocks × ~264 bytes/header = ~587 MB of header data
    in the new snapshot (still well under typical blockchain sizes)
  - The kernel-walk index needs ALL headers, not just the last 2000
  - The trim condition's  check correctly bypasses
    the trim when nHeaders=0

packaging/rpm/build-rpm.sh

@@ -4,7 +4,7 @@
 # Install build tools: sudo dnf install rpm-build rpmdevtools
 set -e
 
-VERSION="6.2.0"
+VERSION="6.2.2"
 RELEASE_URL="https://github.com/SamiAhmed7777/triangles_v5/releases/download/v${VERSION}"
 
 echo "Building RPM for Triangles v${VERSION}..."

packaging/rpm/triangles.spec

@@ -1,5 +1,5 @@
 Name:           triangles
-Version:        6.2.0
+Version:        6.2.2
 Release:        1%{?dist}
 Summary:        Cryptographic Triangles (TRI) cryptocurrency wallet
 License:        MIT