feat(web): charmbracelet-aesthetic tapir spinner with charm palette

Replace the plain ASCII spinner with a Charmbracelet-style TUI panel rendered in
the browser: a dark terminal card holding a rounded purple box (╭─╮╰─╯│) around a
pink block-char tapir (▄▓▀█) with mint eyes (◕ ◕) and a snout that wiggles ∩→∪→~
across three cross-faded frames, plus a lipgloss-style progress bar whose mint
fill grows over a dim track via an 8s CSS clip animation.

Colours come from named palette consts (CharmPurple/Pink/Mint/Cream/Dim) applied
as inline span styles, so the box and CSS share one source of truth. Frames are
built by a small run/line helper that pads each row to a fixed interior width —
an internal test asserts every box row is the same cell width so the border stays
flush. Honours prefers-reduced-motion (static frame + partial bar).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/processing_handler_test.go

@@ -48,8 +48,10 @@ func TestRequestSummarizeImmediateProcessing(t *testing.T) {
 	// The processing card came back while ProcessVideo is still parked on block:
 	// the work runs in a goroutine, the handler did not wait for it.
 	require.Contains(t, html, "Summarizing", "processing card returned")
-	require.Contains(t, html, "ω", "ascii tapir frame rendered")
-	require.Contains(t, html, "∪∪", "all tapir frames rendered")
+	require.Contains(t, html, "╭", "charm box rendered")
+	require.Contains(t, html, "▓", "tapir body block chars rendered")
+	require.Contains(t, html, "∩", "wiggling snout frame rendered")
+	require.Contains(t, html, web.CharmPurple, "charm palette applied to the border")
 	require.Contains(t, html, "/v/"+videoX+"/status", "card polls the status endpoint")
 	require.Contains(t, html, `hx-trigger="every 2s"`, "card auto-polls every 2s")
 	require.NotContains(t, html, "Queued", "not the queue-only card")