docs(33): cause-classified step-down, and a toast that owns the mistake

Design settled with the creator. Two findings drove it:

- **Resolution is not a bandwidth lever.** 1080p30 and 720p60 are both 6 Mbps in the shipped table,
  so "step down to 720p" relieves nothing against congestion; and 60→30 at the same bitrate relieves
  nothing either. Congestion therefore steps **bitrate only** (8.0 → 6.4 → 5.1 → 4.1, ~20%), which is
  what OBS Dynamic Bitrate does — cited, adopted, with its climb-back discarded for v1.
- **The other half has no OBS equivalent**: machine starvation (the game and the app on one PC) steps
  fps, then resolution, and sheds LlamaCasty's own capture cost *first*. That is the app taking
  responsibility for a stream it is helping to starve.

Budgets as ruled: 3 steps for a 1080 start, 1 for 720 and vertical, hard floors at 720p30 /
Vertical 1080p30, hold-and-warn at the floor, never disconnect. Trigger ≥5% drops over 15 s twice,
30 s cooldown, ambiguous evidence does nothing.

New rule in `ui-surface.md`: a toast names the cause, the culprit and the remedy. Mechanism strings
("All pipe instances are busy", HTTP codes, exit codes) are log findings, never user-facing copy.

docs/ai/ui-surface.md

@@ -214,6 +214,12 @@ MIT — notice #10 in `THIRD-PARTY-NOTICES.txt`). Facts that cost a hunt:
 - Calls marshal to the captured Dispatcher (`_dispatcher.Invoke`) — encoder/pump events fire off-thread.
 
 Migrated MessageBoxes: both webcam-acquire warnings, image-read warning, sign-in unsuccessful/failed.
+- **A toast names the cause, the culprit and the remedy (2026-11-09).** A message that reports a
+  mechanism is a bug in the message: "All pipe instances are busy", an HTTP status, an ffmpeg exit
+  code are all findings for the log, not for the creator. Every user-facing message says what
+  happened, **whose fault it was** (the machine, the connection, or LlamaCasty itself), and what the
+  app already did about it. When it is ours, say so plainly — an app that blames the creator's
+  connection for its own starvation is lying, and they will believe it and go buy a new router.
 Promoted from log-only (each keeps its AppLog line): go-live prep failures ×3 (reusable stream,
 broadcast insert, prep exception), frame-pump death while live, mic-missing at startup, premium lapse,
 saved-session refresh failure (sign-out notice). Deliberately left log-only: offline license re-validation