Add Salvium documentation and configuration examples

Co-authored-by: t1amak <57602242+t1amak@users.noreply.github.com>

docs/SALVIUM.md

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+# Salvium Fork Mechanics
+
+This pool implementation includes support for Salvium's unique height-triggered hard fork mechanics. These features are strictly opt-in and maintain 100% backward compatibility with existing coins.
+
+## Configuration
+
+To enable Salvium fork mechanics, add the following to your `config.json`:
+
+```json
+{
+  "coin": "Salvium",
+  "symbol": "SAL",
+  "salvium": {
+    "enabled": true,
+    "addressSeparator": "+",
+    "heights": {
+      "audit_phase1": 815,
+      "audit_phase2": 900,
+      "audit_phase3": 950,
+      "audit_complete": 1000,
+      "require_dual_login": 1050,
+      "carrot": 1100
+    },
+    "addressPrefixes": {
+      "cryptonote": {
+        "public": "0x3ef318",
+        "integrated": "0x55ef318", 
+        "subaddress": "0xf5ef318"
+      },
+      "carrot": {
+        "public": "0x180c96",
+        "integrated": "0x2ccc96",
+        "subaddress": "0x314c96"
+      }
+    },
+    "carrotPoolAddress": "SC1...",
+    "carrotDonationAddress": "SC1..."
+  }
+}
+```
+
+## Fork Mechanics by Height
+
+### Phase 1: Symbol Transition (Height 815)
+- Pool recognizes ticker change from "SAL" to "SAL1"
+- Update config `symbol` field accordingly
+
+### Phase 2: Payout Blackout (Heights 815-999)
+- Miner shares continue to be accepted and credited
+- **Payment processor is disabled** - no payout transactions are sent
+- Balances accumulate normally
+
+### Phase 3: Payout Resume (Heights 1000-1049)
+- Normal payment processing resumes
+- Accumulated balances from blackout period are paid out
+
+### Phase 4: Dual Address Required (Heights 1050-1099)
+- Miners **must** provide dual address format: `[cryptonote_address]+[carrot_address]`
+- Pool rejects single address logins with clear error message
+- Payouts still sent to cryptonote address
+
+### Phase 5: Carrot Payouts (Heights 1100+)
+- All payouts switch permanently to carrot addresses
+- Pool fees/donations use `carrotPoolAddress` and `carrotDonationAddress`
+
+## Miner Instructions
+
+### Before Height 1050
+Use standard cryptonote address:
+```
+your_cryptonote_address
+```
+
+### Heights 1050+
+Use dual address format:
+```
+your_cryptonote_address+your_carrot_address
+```
+
+Example:
+```
+SaLv123...abc+SC1def...xyz
+```
+
+## Address Validation
+
+The pool validates addresses against specific Base58 prefixes:
+
+**Cryptonote Addresses:**
+- Public: 0x3ef318 (SaLv)
+- Integrated: 0x55ef318 (SaLvi)  
+- Subaddress: 0xf5ef318 (SaLvs)
+
+**Carrot Addresses:**
+- Public: 0x180c96 (SC1)
+- Integrated: 0x2ccc96 (SC1i)
+- Subaddress: 0x314c96 (SC1s)
+
+## Backward Compatibility
+
+- **Zero impact** on non-Salvium pools
+- All logic gated behind `config.salvium.enabled` flag
+- Standard cryptonote pools operate unchanged
+- No performance impact when disabled
+
+## Implementation Details
+
+The fork mechanics are implemented in:
+
+- `lib/utils.js`: Core Salvium utility functions
+- `lib/pool.js`: Dual address login validation  
+- `lib/paymentProcessor.js`: Payout blackout and address switching
+- `config.json`: Configuration schema and examples
+
+All changes maintain the existing API and behavior for non-Salvium use cases.