feat(custom-model): generate Run-menu entries from saved endpoint profiles

Follow-up to #393, picking up the work Ark0N invited in his merge comment:
"generate those entries from the saved profiles rather than a fixed
duplicate per harness, and put it in a follow-up PR so this one stays the
backend... The Run-menu picker is yours if you want it."

Adds the frontend surface the backend has been waiting on:

- Run menu: a "Custom Endpoints" section lists one entry per (harness that
  supports customModelInjection, saved endpoint) pair, e.g.
  "Claude Code (llama.cpp)". The harness list comes from
  window.__codemanCustomModelClis, injected at page render straight off the
  CLI registry's own capabilities (never a hardcoded id list in the
  frontend), so a CLI whose injection recipe lands later appears with no
  frontend change. Picking an entry runs that harness's own existing run*()
  function unmodified (case creation, env overrides, everything, forced to
  a single instance) and then applies the endpoint's default model to the
  session it creates via the existing POST /api/sessions/:id/custom-model
  route. Entries are hidden for a remote/docker active case, since that
  route already refuses both.
- Settings: App Settings -> Models gets a "Custom model endpoints" group
  wiring up the customModelEndpointsEnabled toggle (declared since #393,
  read by nothing until now) plus CRUD against the existing
  /api/model-endpoints routes: list, add/edit (inline form), delete,
  discover models.
- Backend: CustomModelHost gains an optional defaultModelId, the model the
  picker applies with no further choice per endpoint (one generated menu
  entry per CLI+endpoint pair, not per CLI+endpoint+model). The route
  refuses a value that isn't one of the endpoint's own discovered models,
  and a fresh discovery drops a default that no longer appears rather than
  carrying an invalid one forward.

Docs: docs/custom-model-endpoints.md describes the new picker and settings
panel; CLAUDE.md's Custom Model Endpoint Profiles entry drops the
"backend-only" status note and documents the picker's generation mechanism.

Tests: four new route tests cover defaultModelId validation, acceptance,
and the drop/keep behaviour across a re-discovery; a new render-index-html
test pins the __codemanCustomModelClis injection (present, agent CLIs
supporting the capability, antigravity and shell excluded) and its
solo-window skip. No browser test was added for the Run-menu picker itself
or the settings CRUD panel (this box has no tmux, so the live server used
by test:browser/test:mobile could not be exercised here) -- worth a
Playwright pass before merge, same as any other frontend PR.

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

src/web/server.ts

@@ -67,7 +67,7 @@ import {
 import { imageWatcher } from '../image-watcher.js';
 import { workflowRunWatcher, summarizeRun } from '../workflow-run-watcher.js';
 import { attachmentRegistry, buildFileThumbnailRoute, registerExternalAttachment } from '../attachment-registry.js';
-import { getCli } from '../config/cli-registry/registry.js';
+import { getCli, enabledClis } from '../config/cli-registry/registry.js';
 import { readCustomModelHosts } from '../custom-model-hosts.js';
 import { applyCustomModelInjection, customModelConfigDir, removeConfigDir } from '../custom-model-injection-apply.js';
 import type { CustomModelBookkeeping } from '../types/session.js';
@@ -1596,6 +1596,18 @@ export class WebServer extends EventEmitter {
         '</head>',
         `<script>window.__codemanCliAvailable=${JSON.stringify(available)};</script>\n</head>`
       );
+      // Which run modes the Run-menu picker (docs/custom-model-endpoints-plan.md) may
+      // generate an entry for: read generically off the registry's `capabilities`
+      // (never an id list here) so a CLI whose customModelInjection lands later shows
+      // up in the picker with no frontend change, and one that ships `unsupported`
+      // (antigravity, and `shell`'s `kind !== 'agent'`) never does.
+      const customModelClis = enabledClis()
+        .filter((entry) => entry.kind === 'agent' && entry.capabilities.customModelInjection.kind !== 'unsupported')
+        .map((entry) => ({ id: entry.id, label: entry.label }));
+      html = html.replace(
+        '</head>',
+        `<script>window.__codemanCustomModelClis=${JSON.stringify(customModelClis)};</script>\n</head>`
+      );
     }
     if (!soloSessionId && process.env.CODEMAN_GESTURE === '1') {
       html = html.replace('</head>', `<script>window.__codemanGestureAvailable=true;</script>\n</head>`);