feat(custom-model): launch directly on the endpoint, no restart, for 7 of 8 CLIs

Fixes the visible double-launch reported on Codex: picking a custom-model
Run-menu entry launched natively first, waited for it to settle, then
restarted it in place with the endpoint applied. Necessary for the design at
the time, but visibly a native boot immediately followed by a second one -
worst on a CLI whose TUI fully reinitializes on a restart, confirmed live on
Codex.

POST /api/quick-start gains an optional customModel field
({endpointId, modelId, confirmed?}). When present, the route mints the
session's id itself (crypto.randomUUID()) before constructing it, computes
the same injection the existing POST /api/sessions/:id/custom-model route
computes (including the llama-swap conflict check from the last commit -
same {requiresConfirmation, currentlyLoadedModel, affectedSessions} shape,
no session created until confirmed), and launches the session already
pointed at the endpoint: env vars via the constructor, and the launchModel
override merged onto piConfig/grokConfig/ompConfig using the registry's own
launch.legacyConfigField the same way session.ts's restart path already
does. No restart at all - setCustomModel() afterward is bookkeeping only.

Wired into 7 of 8 launch functions (session-ui.js): openCode, codex, gemini,
pi, grok, deepseek, omp. Claude stays on the original launch-then-restart
path for now: its own --resume-based restart is far less jarring than the
other seven's, and runClaude()'s multi-tab launch plus docker-config-drift
confirm/retry loop make folding it into the one-shot path separate,
higher-risk work than the other seven's each-a-single-simple-launch shape.

Also fixes a pre-existing 'mode === omp' branch flagged by the CLI-id
static guard (test/cli-registry-no-id-branching.test.ts) - the ompConfig
launchModel merge is the same 'legacy <Mode>Config plumbing' category as
the six sibling branches already allowlisted there, just newly literal
where it was previously only inside resolveOmpConfigForCreate's own check.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RqZeHrRS6DYcGcGX2p9EwG

src/web/schemas.ts

@@ -1033,6 +1033,25 @@ export const QuickStartSchema = z.object({
    * because it takes an existing `workingDir` and so never creates a directory to label.
    */
   agentOrigin: z.string().max(64).optional(),
+  /**
+   * Custom Model Endpoint Profiles (docs/custom-model-endpoints-plan.md): launches directly
+   * on this saved endpoint/model instead of the mode's native backend, computed server-side
+   * from the admin-configured endpoint store the same way `POST /api/sessions/:id/custom-
+   * model` does — never trusting raw env values from the client. One-shot, launch-time
+   * equivalent of that route: no restart, so no visible relaunch (that route's restart-in-
+   * place is still what an ALREADY-RUNNING session uses to switch later). Rejected for
+   * remote/docker cases, same reasoning as `envOverrides` above. `confirmed` mirrors that
+   * route's field: skips the llama-swap "this will unload it for another session" check on
+   * a deliberate retry.
+   */
+  customModel: z
+    .object({
+      endpointId: z.string().regex(/^[a-zA-Z0-9_-]+$/, 'Invalid endpoint id'),
+      modelId: z.string().min(1).max(200),
+      confirmed: z.boolean().optional(),
+    })
+    .strict()
+    .optional(),
 });
 
 // ========== Hook Events ==========