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/custom-model-endpoints.md

@@ -196,14 +196,20 @@ under your thumb:
 - **"Last used"** — shown only when nothing is currently loaded: the model
   actually launched last for this exact (harness, endpoint) pair, read
   from the per-device `codeman:customModelLastUsed:<mode>:<endpointId>`
-  localStorage key. Written by `runCustomModelEntry` /
-  `_quickStartWithCustomModelConfirm` only once the model is actually
-  applied, never on the mere click — declining the context-window warning
-  means this exact model cannot work with this CLI at all, so promoting it
-  next time would be actively wrong, not just premature.
+  localStorage key. Written by `_runCustomModelEntryViaRestart` (claude)
+  and `_quickStartWithCustomModelConfirm` (every one-shot launch; the
+  `runCustomModelEntry` entry point itself only dispatches between the
+  two) only once the model is actually applied, never on the mere click —
+  declining the context-window warning means this exact model cannot work
+  with this CLI at all, so promoting it next time would be actively wrong,
+  not just premature.
 
-Neither tag reorders anything past that one promoted row, and both defer
-to "Default" when neither applies.
+Neither tag reorders anything past that one promoted row. The "Default"
+pill is a separate span, not a third value of the same slot: a promoted
+row that is also the endpoint's `defaultModelId` shows both tags (on a
+single-purpose GPU box that is the common case, and an exclusive slot
+silently dropped the Default marking for exactly that row), and a row
+with neither promotion nor default shows no tag at all.
 
 **How the launch itself applies the endpoint depends on the harness.** For
 opencode, Codex, Gemini, Pi, Grok, DeepSeek and OMP (`runCustomModelEntry` →