feat: rebuild the desktop interface in clipbin's style

Replaces the placeholder shell with a sidebar app in the web Clipbin's look:
a session library, a session timeline (footage, missing and cleaned-up spans,
bookmarks, a draggable clip selection exported on keyframes), clips and
settings. Geist Mono and Lucide icons are embedded. The core gains the
library model and formatting; sample data is opt-in for interface work, and
scripts/rig/screenshot-ui.sh captures each screen headlessly.

scripts/rig/screenshot-ui.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+# Screenshots each Clipbin screen in the headless rig, for reviewing the
+# interface on machines without a display.
+#
+#   scripts/rig/screenshot-ui.sh [output-dir] [screen...]
+#
+# Screens: sessions, session, clips, settings, failed, empty. Uses the sample
+# library (CLIPBIN_SAMPLE_LIBRARY) except for "empty".
+set -euo pipefail
+
+repo="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+out="${1:-${TMPDIR:-/tmp}/clipbin-screens}"
+shift || true
+screens=("$@")
+[[ ${#screens[@]} -eq 0 ]] && screens=(sessions session clips settings failed empty)
+mkdir -p "${out}"
+
+cargo build --locked -p clipbin-desktop --manifest-path "${repo}/Cargo.toml"
+app="${repo}/target/debug/clipbin-desktop"
+
+for screen in "${screens[@]}"; do
+    env=(CLIPBIN_SAMPLE_LIBRARY=1)
+    case "${screen}" in
+        sessions) ;;
+        session) env+=(CLIPBIN_ROUTE=session:2) ;;
+        clips) env+=(CLIPBIN_ROUTE=clips) ;;
+        settings) env+=(CLIPBIN_ROUTE=settings) ;;
+        failed) env+=(CLIPBIN_SAMPLE_STATUS=failed) ;;
+        empty) env=() ;;
+        *) echo "unknown screen ${screen}" >&2; exit 2 ;;
+    esac
+    CLIPBIN_RIG_WIDTH="${CLIPBIN_RIG_WIDTH:-1600}" CLIPBIN_RIG_HEIGHT="${CLIPBIN_RIG_HEIGHT:-1000}" \
+        "${repo}/scripts/rig/headless.sh" bash -c "
+            kill \$(cat \"\${CLIPBIN_RIG_DIR}/game.pid\")
+            env ${env[*]} '${app}' > '${out}/${screen}.log' 2>&1 &
+            sleep 3
+            grim '${out}/${screen}.png'
+            kill %1" 2> /dev/null
+    echo "${out}/${screen}.png"
+done