Feed pagination, duplicate identity detection, pkarr leak fix, Android SAF

Feed pagination:
- Cursor-based pagination: get_feed_page/get_all_posts_page (20 posts/page)
- Batched engagement queries (3 bulk SQL queries instead of 4 per post)
- IntersectionObserver for infinite scroll (sentinel at midpoint)
- Viewport-based media loading (blobs only load when post enters view)
- Pre-fetch next page immediately after current page renders

Duplicate identity detection:
- Anchor detects when a NodeId is already mesh-connected during initial
  exchange and sets duplicate_active flag in response
- Client skips sync tasks when duplicate detected
- Frontend shows red warning banner

Privacy:
- Fixed pkarr leak: clear_address_lookup() removes default dns.iroh.link
  publishing. Only mDNS (local network) discovery enabled.

Android:
- SAF integration via tauri-plugin-android-fs: exports open native "Save As"
  dialog so users can save to Downloads/Drive/etc.
- Download/export paths use app data dir on Android (writable)
- File picker gated behind desktop cfg (blocking_pick not on Android)

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

Cargo.lock

@@ -2732,7 +2732,7 @@ checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
 
 [[package]]
 name = "itsgoin-cli"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "anyhow",
  "hex",
@@ -2744,7 +2744,7 @@ dependencies = [
 
 [[package]]
 name = "itsgoin-core"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "anyhow",
  "base64 0.22.1",
@@ -2767,7 +2767,7 @@ dependencies = [
 
 [[package]]
 name = "itsgoin-desktop"
-version = "0.5.0"
+version = "0.5.1"
 dependencies = [
  "anyhow",
  "base64 0.22.1",
@@ -2780,6 +2780,7 @@ dependencies = [
  "serde_json",
  "tauri",
  "tauri-build",
+ "tauri-plugin-android-fs",
  "tauri-plugin-dialog",
  "tauri-plugin-notification",
  "tokio",
@@ -5623,6 +5624,20 @@ dependencies = [
  "walkdir",
 ]
 
+[[package]]
+name = "tauri-plugin-android-fs"
+version = "8.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c63a3cf10132c76d0194cb229411a12d9af4493f15695a27bbe5ab184f20d711"
+dependencies = [
+ "serde",
+ "serde_json",
+ "tauri",
+ "tauri-plugin",
+ "tauri-plugin-fs",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "tauri-plugin-dialog"
 version = "2.7.0"