improve gmail sync: email input, permanent errors, auto-dock

- add isync to setup.sh
- ask for gmail address alongside app password in integrations
- add PermanentError to job queue (skips retries for non-recoverable failures)
- use PermanentError for missing credentials, missing executable, auth failures
- auto-add /email to dock after successful gmail sync
- invalidate dock cache on sync completion for seamless UI update

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/setup.sh

@@ -135,6 +135,15 @@ if has sqlite3; then skip "sqlite3"; else
   esac
 fi
 
+# isync (provides mbsync for Gmail IMAP sync)
+if has mbsync; then skip "isync (mbsync)"; else
+  case $PM in
+    apt)    CORE_PKGS+=(isync) ;;
+    pacman) CORE_PKGS+=(isync) ;;
+    brew)   CORE_PKGS+=(isync) ;;
+  esac
+fi
+
 # ripgrep
 if has rg; then skip "ripgrep"; else
   case $PM in