explorer: add no-sync mode details to explorer quick start guides

Updates include:
- Updated `explorer/README` quick start guide with instructions on starting an explorer environment (site + explorerd) in no-sync mode (skipping blockchain node connections)
- Updated `explorer/explorerd/README` quick start guide with details on running `explorerd` in no-sync mode

bin/explorer/README.md

@@ -71,6 +71,16 @@ make start-testnet
 make start-mainnet
 ```
 
+### Start Explorer Environment in No-Sync Mode
+An explorer environment can be started in a no-sync mode that does not connect a darkfi blockchain network or sync new blocks, allowing you to work with an existing local explorer database. This feature is particularly useful for UI development, testing, development tasks that don't require syncing, or exploring functionality without the overhead of running a blockchain network.
+
+Below is an example of how to launch a no-sync environment configured for localnet. You can also start testnet or mainnet similarly (using `start-no-sync-testnet` or `start-no-sync-mainnet`):
+
+```sh
+# Launch localnet explorer environment without connecting or syncing with a Darkfi blockchain network
+make start-no-sync-localnet
+```
+
 > **Note** Once started, navigate to http://127.0.0.1:5000 in your browser to access the explorer interface.
 
 ### Confirming Successful Start
@@ -97,6 +107,7 @@ Started localnet environment. Press Ctrl-C to stop.
 ```
 
 > **Note** Localnet explorer site logs appear directly in the console, while testnet and mainnet logs are written to `~/.local/share/darkfi/explorer_site/{network}/app.log`. For non-localnet environments, the console displays: `See site logfile /home/user/.local/share/darkfi/explorer_site/{network}/app.log for server startup details`.
+> **Note** In no-sync mode, you will see “Started DarkFi Explorer Node (No-Sync Mode)” in the banner header, and the “Connected Darkfi Node:” line will show “Not connected”.
 
 The explorer site log contains the following statup details.
 ```

bin/explorer/explorerd/README.md

@@ -51,6 +51,16 @@ make start-testnet
 make start-mainnet
 ```
 
+### Start in No-Sync Mode
+You can run explorerd in a no-sync mode that does not connect to any nodes or sync blocks. This approach is useful if you only need to work with an existing local explorer database, perform tests, or work on the site UI without running blockchain nodes or miners (which can be resource-intensive).
+
+Below is an example of how to launch a no-sync environment for localnet. You can also start testnet or mainnet in the same manner (for example, using `start-no-sync-testnet` or `start-no-sync-mainnet`).
+
+```sh
+# Launch an explorer without connecting to or syncing with any blockchain nodes
+make start-no-sync-localnet
+```
+
 ### Stopping the Node
 
 ```sh
@@ -77,6 +87,7 @@ When a DarkFi Explorer Node successfully starts, users should a startup banner d
 03:31:37 [INFO]   - Connected Darkfi Node: tcp://127.0.0.1:8240
 03:31:37 [INFO] ========================================================================================
 ```
+> **Note** In no-sync mode, you will see “Started DarkFi Explorer Node (No-Sync Mode)” in the banner header, and the “Connected Darkfi Node:” line will show “Not connected”.
 
 ### Getting Help
 ```shell