Release: model-picker Selected badge + Transparent Stream dupe-prefix suppression (#5757, #5758) (#5850)

Two visible render PRs, gate-passed (deep-review round), Nathan-approved to ship.

- #5757 (rodboev): mark active model with a Selected badge + open its provider group (#5748).
  Screenshot-verified (badge clear + correctly placed on active row).
- #5758 (rodboev): suppress the live-token prose row that is a strict prefix of the final
  answer (#5749). Provenance-gated (live-prose:* token rows after last tool row only) so it
  can't eat legitimate narration; reproduction test proves the dupe is gone.

Codex SAFE + full regression green (1576 render tests). 18 own tests pass together.

Co-authored-by: t <a@b>
Co-authored-by: rodboev <rodboev@users.noreply.github.com>

static/style.css

@@ -3237,7 +3237,7 @@
 .ws-dropdown{display:none;position:absolute;bottom:calc(100% + 4px);left:0;right:0;min-width:200px;background:var(--surface);border:1px solid var(--border2);border-radius:10px;box-shadow:0 -4px 24px rgba(0,0,0,.4);z-index:200;overflow:hidden;max-height:320px;overflow-y:auto;}
 .ws-dropdown.open{display:block;}
 .ws-dropdown-footer{left:0;right:auto;bottom:calc(100% + 4px);min-width:280px;max-width:min(420px,calc(100vw - 32px));}
-.model-dropdown{display:none;position:absolute;bottom:calc(100% + 4px);left:0;min-width:280px;max-width:min(420px,calc(100vw - 32px));background:var(--surface);border:1px solid var(--border2);border-radius:10px;box-shadow:0 -4px 24px rgba(0,0,0,.4);z-index:200;overflow:hidden;max-height:320px;overflow-y:auto;}
+.model-dropdown{display:none;position:absolute;bottom:calc(100% + 4px);left:0;min-width:280px;max-width:min(420px,calc(100vw - 32px));background:var(--surface);border:1px solid var(--border2);border-radius:10px;box-shadow:0 -4px 24px rgba(0,0,0,.4);z-index:200;overflow:hidden;max-height:min(70vh,640px);overflow-y:auto;}
 .model-dropdown.open{display:block;}
 .model-scope-note{position:sticky;top:0;z-index:2;padding:9px 14px;border-bottom:1px solid var(--border);color:var(--text);font-size:11px;font-weight:650;line-height:1.4;background:color-mix(in srgb,var(--surface) 82%,var(--accent-bg));box-shadow:0 1px 0 rgba(0,0,0,.12);}
 .model-group{padding:8px 14px 4px;font-size:10px;font-weight:700;letter-spacing:.04em;color:var(--muted);text-transform:uppercase;border-top:1px solid var(--border2);margin-top:2px;}.model-group.collapsible{cursor:pointer;user-select:none}.model-group.collapsible:before{content:'\25b6';display:inline-block;font-size:8px;margin-right:5px;transition:transform .15s ease}.model-group.collapsible.open:before{transform:rotate(90deg)}.model-group-body:empty{display:none}
@@ -3252,6 +3252,7 @@
 .model-opt-badge{display:inline-flex;align-items:center;justify-content:center;padding:2px 7px;border-radius:999px;font-size:10px;font-weight:700;letter-spacing:.02em;text-transform:uppercase;border:1px solid transparent;}
 .model-opt-badge--primary{background:rgba(50,184,198,.16);border-color:rgba(50,184,198,.32);color:#8fe7ef;}
 .model-opt-badge--fallback{background:rgba(255,184,77,.14);border-color:rgba(255,184,77,.28);color:#ffd18a;}
+.model-opt-badge--selected{background:rgba(99,179,255,.16);border-color:rgba(99,179,255,.34);color:#cfe8ff;}
 .model-opt-id{display:block;font-size:10px;color:var(--muted);line-height:1.3;opacity:.72;word-break:break-word;}
 .model-provider-hint{margin:2px 14px 6px;padding:7px 9px;border:1px solid var(--border2);border-radius:7px;background:color-mix(in srgb,var(--surface) 90%,var(--warning));color:var(--muted);font-size:11px;line-height:1.35;}
 .model-opt-provider{display:inline-flex;align-items:center;padding:1px 6px;border-radius:4px;font-size:9px;font-weight:600;letter-spacing:.03em;color:var(--muted);background:rgba(255,255,255,.05);border:1px solid var(--border2);margin-left:auto;white-space:nowrap;flex-shrink:0;}