reorder transaction detail view: txid first, logical grouping with separators

Reorganize the transaction detail view into logical blocks separated by
thin horizontal rules:

- Identity: transaction hash (first!), type, status
- Timing: time, block number
- Value: amount, native quantity, token contract, from, to
- Decoded details: action/protocol/steps (contract calls)
- Network details: nonce, gas price, gas used, fee
- Raw data: full calldata

Updates README screen map to reflect new field ordering and grouping.

closes #131

README.md

@@ -435,25 +435,35 @@ transitions.
 #### TransactionDetail
 
 - **When**: User tapped a transaction row from AddressDetail or AddressToken.
-- **Elements**:
+- **Elements** (grouped into logical blocks separated by thin rules):
     - "Transaction" heading, "Back" button
-    - Type: transaction classification — one of: Native ETH Transfer, ERC-20
-      Token Transfer, Swap, Token Approval, Contract Call, Contract Creation
-    - Token contract: shown for ERC-20 transfers — color dot + full contract
-      address (tap to copy) + etherscan token link
-    - Status: "Success" or "Failed"
-    - Time: ISO datetime + relative age in parentheses
-    - Amount: value + symbol (bold)
-    - From: blockie + color dot + full address (tap to copy) + etherscan link
-        - ENS name if available
-    - To: blockie + color dot + full address (tap to copy) + etherscan link
-        - ENS name if available
-    - Transaction hash: full hash (tap to copy) + etherscan link
-    - Block: block number (tap to copy) + etherscan block link
-    - Nonce: transaction nonce (tap to copy)
-    - Transaction fee: ETH amount (tap to copy)
-    - Gas price: value in Gwei (tap to copy)
-    - Gas used: integer (tap to copy)
+    - **Identity block**:
+        - Transaction hash: full hash (tap to copy) + etherscan link
+        - Type: transaction classification — one of: Native ETH Transfer,
+          ERC-20 Token Transfer, Swap, Token Approval, Contract Call,
+          Contract Creation
+        - Status: "Success" or "Failed"
+    - **Timing block**:
+        - Time: ISO datetime + relative age in parentheses
+        - Block: block number (tap to copy) + etherscan block link
+    - **Value block**:
+        - Amount: value + symbol (bold)
+        - Native quantity: raw integer + unit (shown when available)
+        - Token contract: shown for ERC-20 transfers — color dot + full
+          contract address (tap to copy) + etherscan token link
+        - From: blockie + color dot + full address (tap to copy) + etherscan
+          link; ENS name if available
+        - To: blockie + color dot + full address (tap to copy) + etherscan
+          link; ENS name if available
+    - **Decoded details** (shown for contract calls):
+        - Action name, decoded parameters, token details, swap steps
+    - **Network details** (shown when on-chain data is available):
+        - Nonce: transaction nonce (tap to copy)
+        - Gas price: value in Gwei (tap to copy)
+        - Gas used: integer (tap to copy)
+        - Transaction fee: ETH amount (tap to copy)
+    - **Raw data** (shown when calldata is present):
+        - Full calldata in monospace dashed border
 - **Transitions**:
     - "Back" → **AddressToken** (if `selectedToken` set) or **AddressDetail**