refactor: centralize constants, eliminate unwraps, remove dead code, resolve TODOs

- R13+R16: Replace .expect() with .context()? in main.rs and identity.rs
- R17+R18+R19: Fix unwrap() calls in helpers and js-engine
- R20+R21: Remove #[allow(dead_code)] annotations and delete truly dead code
- R22-R26: Create constants.rs module, replace 21 hardcoded values across 12 files
- R28+R29: LND/DWN timeouts already present — verified
- R30-R33: Remove TODO comments, implement marketplace payment check

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/network/dwn_sync.rs

@@ -73,7 +73,7 @@ pub async fn get_dwn_status() -> Result<DwnStatusResponse> {
         .context("Failed to build HTTP client")?;
 
     let res = client
-        .get("http://127.0.0.1:3100/health")
+        .get(crate::constants::DWN_HEALTH_URL)
         .send()
         .await
         .context("DWN server not reachable")?;
@@ -108,7 +108,7 @@ pub async fn sync_with_peers(data_dir: &Path, peer_onions: &[String]) -> Result<
     state.status = SyncStatus::Syncing;
     save_sync_state(data_dir, &state).await?;
 
-    let socks_proxy = reqwest::Proxy::all("socks5h://127.0.0.1:9050")
+    let socks_proxy = reqwest::Proxy::all(crate::constants::TOR_SOCKS_PROXY)
         .context("Failed to create SOCKS proxy")?;
 
     let client = reqwest::Client::builder()