feat(quality): the creator sets the rate — per tier, persisted, clamped only at YouTube's floor

The tier table cannot know a creator's connection, so it should not pretend to. The
Mbps box under the picker is theirs: the tier chooses geometry and frame rate, the
box chooses bits. Stored per tier (`Video.Rate.<tier>`), so tuning 1080p60 does not
touch 720p30, and none means "the shipped default" rather than zero.

Clamped at the tier's YouTube minimum (`RateLadder`), because a target under it
cannot hold the resolution; no ceiling otherwise, because a wrong guess is exactly
what live step-down exists to catch, and a creator who types 25 on a fibre line
should be allowed to find out. The tooltip carries YouTube's number for the tier.

`MainViewModel.EffectiveQuality` is the single substitution point, and the encoder
options, the step-down policy and the clip buffer all read it — so a rated tier can
never stream at the shipped default because one call site was missed.

One ordering trap found by the test: the constructor resolves the default tier
before the layout store is open, so a read at that point must not cache, or the
shipped default shadows the creator's stored rate for the whole run.

670 pass, 0 warnings.

docs/ai/ui-surface.md

@@ -144,7 +144,7 @@ Placement math itself is covered by `WindowPlacementTests` (pure function, no HW
   geometry fields are 44px: the measured width of `-1920` in the app's font at 11px (via WPF's
   `FormattedText` — **measure, don't guess**) plus the field's padding and border. Guard:
   `ytLive.Tests/GeometryFieldWidthTests.cs`
-- Resolution tiers: 1080p60@12 (default) → 1080p30@10 → 720p60@6 → 720p30@6 → **Vertical 1080p30@10 and 1080p60@12 (9:16, 1080×1920)** — the `@` is the CBR target the encoder is asked to hold, between YouTube's H.264 recommendation and the practitioner sweet spot (its 14/17/8 recommendations are the max, the tier minimums 5/6/3 the step-down floor). Vertical mirrors its landscape pair: same pixel count, same rate. The old flat 8 Mbps was an inherited round number, not a measurement. The composition master frame is **always 1920×1080** — a tier is an output rect + target resolution over that master, so source geometry is never rewritten (no rounding drift). 16:9 tiers use the full frame; vertical tiers use a centered **607×1080** window and the preview dims the cropped side strips at 55% black with an accent outline (semi-crop — the cut area stays visible). A resolution badge in the preview corner shows the active tier. The resolution picker and live readouts (bitrate/FPS/dropped/duration) are in the top-left cell above the layers panel; the bottom bar is an empty height-preserving spacer. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable). The future encoder crops the master to the rect and scales to the tier's Width×Height
+- Resolution tiers: 1080p60@12 (default) → 1080p30@10 → 720p60@6 → 720p30@6 → **Vertical 1080p30@10 and 1080p60@12 (9:16, 1080×1920)** — the `@` is the CBR target the encoder is asked to hold, between YouTube's H.264 recommendation and the practitioner sweet spot (its 14/17/8 recommendations are the max, the tier minimums 5/6/3 the step-down floor). Vertical mirrors its landscape pair: same pixel count, same rate. The old flat 8 Mbps was an inherited round number, not a measurement. The composition master frame is **always 1920×1080** — a tier is an output rect + target resolution over that master, so source geometry is never rewritten (no rounding drift). 16:9 tiers use the full frame; vertical tiers use a centered **607×1080** window and the preview dims the cropped side strips at 55% black with an accent outline (semi-crop — the cut area stays visible). A resolution badge in the preview corner shows the active tier. The resolution picker and live readouts (bitrate/FPS/dropped/duration) are in the top-left cell above the layers panel; the bottom bar is an empty height-preserving spacer. Under the picker sits the creator's own **rate box** (Mbps, per tier, persisted as `Video.Rate.<tier>`): the tier chooses geometry, the box chooses bits, clamped at the tier's YouTube minimum and otherwise unbounded because live step-down is the thing that catches a wrong guess. Its tooltip carries YouTube's recommendation for the tier (`Models/RateLadder`). Every consumer — encoder options, step-down policy, clip buffer — reads `MainViewModel.EffectiveQuality`, never the raw tier. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable). The future encoder crops the master to the rect and scales to the tier's Width×Height
 - **Locked output tiers stay visible and clickable.** They are dimmed for non-owners. Choosing one keeps the free tier selected and opens About in-app; only the explicit llamacasty.com link opens a browser.
 - Crash diagnosis: `AppLog` writes startup checkpoints to `%APPDATA%\ytLlive\startup.log`; `App.xaml.cs` logs `DispatcherUnhandledException`/`AppDomain.UnhandledException`. When WPF won't run from WSL, this log is how you find the failure (it caught the `MenuItemRole.Separator` XAML crash and the ComboBox SelectionBoxItem bug). **The log is SIZE-CAPPED (TASK 55, 2026-10-22):** at 5 MB `startup.log` rolls to `startup.1.log` (one rolled copy kept) — the policy lives in `Helpers/LogRotation.cs` as a pure function over a path, so `AppLog`'s 156-call-site surface never changes and the rule is testable on its own. Guard: `ytLive.Tests/AppLogRotationTests.cs`