fix(custom-model): merge-time fixes for the promoted-model picker (#459)

The maintainer's promised follow-ups to opticon454's picker promotion,
applied on the landing branch after the merge (ecb95b5d):

- session-ui.js: the promotion tag ("Currently loaded" / "Last used") and
  the "Default" pill are two separate spans, so a promoted row that is
  also the endpoint's defaultModelId shows both instead of silently
  losing its Default marking; two tests pin it (both fail on the old
  exclusive-slot rendering).
- styles.css: a dedicated #customModelPickModal .set-scope rule, since
  the pill was only styled inside the three settings modals and rendered
  as plain body text here; same skin tokens, modal layout untouched.
- docs/wiki/Custom-Model-Endpoints.md: describe the promotion (currently
  loaded, else last used per device), the separate Default pill, and
  that nothing is ever auto-chosen.
- CLAUDE.md + docs/custom-model-endpoints.md: credit the real "Last used"
  writers (_runCustomModelEntryViaRestart and
  _quickStartWithCustomModelConfirm; runCustomModelEntry only dispatches
  since 88e5b7b2) and drop the now-wrong "both defer to Default" sentence.
- Not done: moving the one-shot "last used" write into
  _runCustomModelEntryOneShot, because the existing one-shot tests assert
  that _quickStartWithCustomModelConfirm writes the key itself.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
(cherry picked from commit 0cb0f911adc14a852ba5c2951768a4aa87c25657)

docs/wiki/Custom-Model-Endpoints.md

@@ -50,7 +50,13 @@ pointed at.
 the session launches straight away on that model — nothing to choose. With two or more, a
 small dialog asks which one to use for this launch before starting the session; the
 endpoint's default model, if set, is marked but not auto-picked, so a launch can deliberately
-use a different one without changing the saved default.
+use a different one without changing the saved default. The list is not raw discovery order
+either: the model llama-swap reports loaded and ready is moved to the top and tagged
+**Currently loaded**, and when nothing is loaded, the model you last launched on this harness
+and endpoint pair is moved up instead and tagged **Last used** (a per-device browser value, so
+another device starts from its own history). The default model keeps its own **Default** pill
+in both cases, and nothing is ever auto-chosen: the promoted row is simply the one under your
+thumb.
 
 **For opencode, Codex, Gemini, Pi, Grok, DeepSeek and OMP, picking an entry launches
 straight onto the endpoint** — no restart, because the endpoint is applied before the