fix(custom-model): address third pre-merge review (Ark0N)

Blocker 1: the loading banner hides itself ~200ms after it reopens.

- _showCenterStatus reuses one shared DOM node; dismiss() scheduled
  el.hidden = true 200ms later with nothing to cancel it. On the
  Claude path, switchingToast.dismiss() is followed by one same-
  origin request (5-30ms locally) before _watchLlamaSwapLoading opens
  the new banner -- well inside that window -- so the stale timer
  fired against the shared node and hid the fresh banner, leaving the
  whole model-load wait with no progress text, no log line and no
  reachable Cancel button.
- Fixed by parking the pending timeout on the element and clearing it
  at the top of _showCenterStatus. Added a regression test that
  reproduces the exact repro (open, dismiss, reopen 20ms later,
  advance past 200ms) alongside the existing Cancel-button DOM tests;
  confirmed it fails without the fix and passes with it.

Blocker 2: the swap-conflict warning named other users' sessions.

- Both affectedSessions scans (POST .../custom-model and quick-start)
  walked the whole session map with no ownership filter, so in multi-
  user mode a non-admin pointing their own session at a shared
  endpoint learned another user's session name and id -- which with
  autoNameSessions on is that user's own prompt.
- The swap is still blocked pending confirmation regardless of
  ownership (a foreign session is just as real a disruption); only
  which ones get NAMED back to the caller is scoped, via the
  already-imported canAccessOwned. Added a two-owner test to
  test/routes/session-custom-model.test.ts covering both the
  foreign-owner (blocked, not named) and same-owner (named) cases.

Smaller ride-along fixes:

- server.ts boot recovery now passes contextLength into
  applyCustomModelInjection, so CLAUDE_CODE_MAX_CONTEXT_TOKENS is
  correctly rebuilt into _envOverrides after a restart instead of
  surviving only because tmux retains the old setenv.
- pumpLlamaSwapLogTail's finally now deletes by IDENTITY, not just by
  key, so an aborted pump finishing after a newer entry was created
  for the same endpoint can no longer delete that newer entry and
  orphan its connection.
- docs/custom-model-endpoints.md now notes that clearing a custom
  model removes injected keys by name, including CLAUDE_CONFIG_DIR --
  so a session that also had CLAUDE_CONFIG_DIR set via envOverrides
  (the per-client-account case) silently falls back to the default
  account on clear.

Left for later, as flagged in the review itself: the quick-start
case-scaffolding/cancel ordering (real behavioural reordering across
a large handler, too risky to make without a live re-test), and
retiring runCustomModelEntry's mode === 'claude' branch behind a
launchStrategy registry field (explicitly deferred by the reviewer to
"the next one").

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ea59JhUmHBm1gRCsiYF33R

src/web/public/panels-ui.js

@@ -5583,12 +5583,21 @@ Object.assign(CodemanApp.prototype, {
       el.id = 'customModelCenterStatus';
       document.body.appendChild(el);
     }
+    // A pending hide from a PREVIOUS dismiss() (e.g. switchingToast.dismiss() right
+    // before this same-origin call reopens the banner within its 200ms fade) must
+    // never fire against the node this call is about to show — clear it before
+    // reusing the shared DOM node, or the old timer hides the fresh banner ~200ms in.
+    if (el._hideTimer) {
+      clearTimeout(el._hideTimer);
+      el._hideTimer = null;
+    }
     el.className = `center-status-banner center-status-${type}`;
     el.innerHTML = '';
     const dismiss = () => {
       el.classList.remove('show');
-      setTimeout(() => {
+      el._hideTimer = setTimeout(() => {
         el.hidden = true;
+        el._hideTimer = null;
       }, 200);
     };
     if (type !== 'error') {