fix: add producer signature and pubkey verification in P2P block sync

- Import Ed25519PublicKey for signature verification
- Add address_from_pubkey helper
- Implement _verify_block_signature and _verify_miner_pubkey_match
- Call these in validate_block before accepting block

This fixes critical consensus vulnerability where P2P sync accepted forged blocks without checking signatures or producer authorization.

Fixes #2001

Bounty: Critical (100-150 RTC)
Wallet: RTC3fcd93a4ec68cfd6b59d1b41c4872c5c239c4ad8

Author: penggaolai

.github/ISSUE_TEMPLATE/bounty-claim.yml

@@ -1,59 +1,59 @@
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+name: Bounty Claim
+description: Claim an RTC bounty for your contribution
+title: "[Bounty Claim] "
+labels: [bounty-claim]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        ## Claim an RTC Bounty
+        Fill out this form after your PR is merged to receive your RTC payment.
+        **Reference rate: 1 RTC = $0.10 USD**
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.github/ISSUE_TEMPLATE/bug-report.yml

@@ -1,82 +1,82 @@
-name: Bug Report
-description: Report a bug in RustChain node, miner, or wallet
-title: "[Bug] "
-labels: [bug]
-body:
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+title: "[Bug] "
+labels: [bug]
+body:
+  - type: markdown
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+        ## Report a Bug
+        Thanks for helping improve RustChain! Bug fixes can earn RTC bounties.
+
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+    id: component
+    attributes:
+      label: Component
+      options:
+        - Node (rustchain_v2_integrated)
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