refactor(config): centralize remaining magic numbers and finalize log hygiene

Add comprehensive TransportConfig constants for UI, Nostr, and BLE; adopt across ChatViewModel, ContentView, BLEService, ShareViewController, and BitchatApp to remove scattered literals. Standardize Nostr lookbacks/limits, UI delays/animations, and BLE announce/duty-cycle/candidate caps. Preserve behavior while making tuning explicit and safe.

Highlights:\n- UI: animations, scroll throttle, long-message thresholds, batch stagger, color hue tuning, rate-limit buckets, read-receipt debounce, startup delays, share accept/dismiss windows, migration cutoff.\n- Nostr: short display length (8), conv-key prefix length (16), DM lookback (24h), geohash sample lookback/limits; consistent use throughout ChatViewModel.\n- BLE: dynamic RSSI defaults, announce intervals/base+jitter, duty cycles (dense/sparse), fragment/ingress lifetimes, expected write timings/spacing, recent packet window (30s/100), peer inactivity timeout; unified candidate caps (100).\n- Share: use constant dismiss delay; App: use constant share accept window.\n\nRisk/impact: behavior-equivalent with centralized knobs; easier to tune without code edits.

bitchatShareExtension/ShareViewController.swift

@@ -159,7 +159,7 @@ final class ShareViewController: UIViewController {
     private func finishWithMessage(_ msg: String) {
         statusLabel.text = msg
         // Complete shortly after showing status
-        DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
+        DispatchQueue.main.asyncAfter(deadline: .now() + TransportConfig.uiShareExtensionDismissDelaySeconds) {
             self.extensionContext?.completeRequest(returningItems: nil, completionHandler: nil)
         }
     }