feat: uBlock Origin Lite integration for ad-blocking during WebPage captures

- singlefile.rs: when ARCHIVR_UBLOCK=true and ARCHIVR_UBLOCK_EXT is set,
  archivr owns Chrome's lifecycle (--headless=new, --remote-debugging-port,
  --load-extension); single-file connects via --browser-server instead of
  launching its own Chrome. Falls back to old behaviour with ublock_skipped=true
  when the ext path is missing or invalid.
- capture.rs: thread ublock_skipped through CaptureResult
- database.rs: add notes_json TEXT column to capture_jobs (DDL + idempotent
  ALTER TABLE migration); update_capture_job_status gains notes_json param
- archive.rs: expose notes_json in CaptureJobSummary
- routes.rs: store {"ublock_skipped":true} in notes_json on completed captures
- ToastStack.jsx: warning toast variant (toast--warning) with Details expander
  and Ignore button
- CaptureDialog.jsx: fire warning toast when poll result has ublock_skipped
- App.jsx: sessionStorage-backed Ignore suppression for ublock warnings
- styles.css: .toast--warning (amber left border) + .toast-warning-detail
- flake.nix: ublockLite derivation fetches uBOLite_2026.705.2152.chromium.zip
  (pinned SHA256) from uBlockOrigin/uBOL-home; sets ARCHIVR_UBLOCK_EXT in both
  archivr and archivr-server wrappers

Env vars:
  ARCHIVR_UBLOCK=true (default) — enable uBlock during WebPage captures
  ARCHIVR_UBLOCK_EXT — path to unpacked uBOL extension dir (set by Nix)

flake.nix

@@ -60,6 +60,22 @@
           tweetPython = pkgs.python312.withPackages (ps: [
             twitterApiClient
           ]);
+          # uBlock Origin Lite (MV3) — unpacked Chromium extension for headless ad-blocking.
+          # Fetched from the uBOL-home GitHub releases; update version + hash together.
+          ublockLite = pkgs.stdenv.mkDerivation {
+            pname = "ublock-origin-lite";
+            version = "2026.705.2152";
+            src = pkgs.fetchurl {
+              url = "https://github.com/uBlockOrigin/uBOL-home/releases/download/2026.705.2152/uBOLite_2026.705.2152.chromium.zip";
+              hash = "sha256-4TbvDYbkOkDuVK17TeAbLDBcgf9O6f/vh2buGbLu4XQ=";
+            };
+            nativeBuildInputs = [ pkgs.unzip ];
+            sourceRoot = ".";
+            installPhase = ''
+              mkdir -p $out
+              cp -r . $out/
+            '';
+          };
           version = "0.1.0";
           src = pkgs.lib.cleanSource ./.;
           cargoLock = {
@@ -123,6 +139,7 @@
                 ${lib.optionalString pkgs.stdenv.isLinux "--set ARCHIVR_CHROME ${pkgs.chromium}/bin/chromium"} \
                 --set ARCHIVR_TWEET_PYTHON ${tweetPython}/bin/python3 \
                 --set ARCHIVR_TWEET_SCRAPER $out/libexec/archivr/scrape_user_tweet_contents.py \
+                --set ARCHIVR_UBLOCK_EXT ${ublockLite} \
                 --prefix PATH : ${
                   lib.makeBinPath ([
                     pkgs.yt-dlp
@@ -149,7 +166,8 @@
                 --set ARCHIVR_SINGLE_FILE ${pkgs.single-file-cli}/bin/single-file \
                 ${lib.optionalString pkgs.stdenv.isLinux "--set ARCHIVR_CHROME ${pkgs.chromium}/bin/chromium"} \
                 --set ARCHIVR_TWEET_PYTHON ${tweetPython}/bin/python3 \
-                --set ARCHIVR_TWEET_SCRAPER $out/libexec/archivr-server/scrape_user_tweet_contents.py
+                --set ARCHIVR_TWEET_SCRAPER $out/libexec/archivr-server/scrape_user_tweet_contents.py \
+                --set ARCHIVR_UBLOCK_EXT ${ublockLite}
             '';
           };
           archivr-all = pkgs.symlinkJoin {