fix: creator feedback batch Branch 1 — TRAX volume, tooltip, meter boost, slider click, backdrop

- TRAX: LocalGain now applies 0.2× factor so music is quieter relative to desktop audio slider
- TRAX tooltip: switched to ToolTipService with Placement=Top to fix z-order in Viewbox overlay
- Mic meter: MeterLevel multiplied by 1.2× before clamping for ~20% higher visual readout
- Volume sliders: click anywhere on track to jump thumb to that position before dragging
- Backdrop: Image Visibility now binds to BackdropVisible; compositor checks IsVisible before blit
- Renamed 'Backdrop' to 'Game Capture' in EnsureBackdrop + test assertions

HANDOFF.md

@@ -5,10 +5,10 @@
 > a problem. Conventions: [`schema.md`](schema.md). Rewrite this file at session
 > end, compaction, or any interruption.
 
-## Session state (last updated: 2026-08-16, renumbering finalised)
+## Session state (last updated: 2026-08-17, creator feedback batch Branch 1)
 
-- **Branch:** `main`, tracking `origin/main`. Working tree: the **TASK 9 reusable-stream slice** is
-  committed + pushed (details below). Local branches `social-bar`/`webcam-validation` untouched (no secrets).
+- **Branch:** `main`, tracking `origin/main`. Working tree: **TASK 14 Branch 1 (quick fixes)** — TRAX volume, tooltip, mic meter boost, click-to-position sliders, backdrop visibility + rename. Build **0 warnings**, **207 tests passing**. Ready to commit.
+- **TASK 14 — CREATOR FEEDBACK BATCH — IN PROGRESS.** Branch 1 shipped: TRAX volume 0.2× factor, TRAX tooltip z-order fix, mic meter +20% boost, click-to-position volume sliders, backdrop visibility binding + compositor guard, rename "Backdrop" → "Game Capture". Branch 2 pending: Elements panel, webcam border config, Countdown source (Starting/BRB), Web source.
 - **TASK 9 — REUSABLE STREAM + HEALTH BANNER — SHIPPED 2026-08-16 (items 1–3).**
   - **Items 1–2 (reusable stream):** `_rtmpUrlProvider` now yields a real RTMP URL.
     `YouTubeStreamService` gains `GetOrCreateReusableStreamAsync` (lists `liveStreams?mine=true`,
@@ -40,9 +40,7 @@
 - **TASK 13 added** — marcom/launch kit. Business details moved to `MARCOM.md`. Queued after all v1 features.
 - **Backlog updated** — removed v0.3 (stream scheduling, not needed for casual streamers). Multi-destination
   restreaming noted as "congrats, you're ready for OBS" moment.
-- **Resume point (next branch):** **TASK 9 item 4 — live chat** (`liveChat/messages` poll, right-panel
-  render, Super Chat + membership badges). Then item 5 (error handling), item 6 (visibility unlock),
-  item 7 (full broadcast form), then TASK 10 (billing + unlock + support).
+- **Resume point (next branch):** **TASK 14 Branch 2** — Elements panel beneath Sources (per-element config with live preview, ✕ revert / ✓ commit), webcam border config (color #RRGGBB + picker, thickness 0–10), Countdown source (Starting/BRB scenes, timer 1–60 min), Web source (all scenes, URI input). Then **TASK 9 item 4 — live chat**.
 - **TASK 12 — MASTER LIMITER — COMMITTED + PUSHED 2026-08-15.** Queued from the TRAX discussion: the
   live mix summed mic + loopback with no ceiling, so hot gains could pass 0 dBFS and clip the AAC
   encode. New pure `Services/Audio/MasterLimiter.cs` (−1 dBFS ceiling, instant attack per frame,