feat: custom endpoint fields in new profile form (fixes #170, closes #214)

* feat: add custom endpoint fields to new profile form

* fix: skip config write tests when PyYAML not installed

The 4 unit tests for _write_endpoint_to_config imported yaml directly
without handling ImportError. Added pytest.importorskip('yaml') at
module level so the entire test class skips cleanly in environments
without PyYAML. Removed redundant per-method yaml imports.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: wire frontend for custom endpoint fields in new profile form

- Add Base URL and API key inputs to the profile create form (index.html)
- Wire panels.js submitProfileCreate() to send base_url and api_key
- Clear new fields on form toggle/cancel
- Add client-side URL format validation (must start with http:// or https://)
- Add server-side URL format validation in routes.py (400 for invalid scheme)
- Add test_api_route_rejects_invalid_base_url() covering the new validation
- Base URL input has placeholder 'http://localhost:11434' per review suggestion

---------

Co-authored-by: Nathan Esquenazi <nesquena@gmail.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/index.html

@@ -123,6 +123,8 @@
         <label style="display:flex;align-items:center;gap:6px;font-size:11px;color:var(--muted);margin-bottom:8px;cursor:pointer">
           <input type="checkbox" id="profileFormClone" style="accent-color:var(--accent)"> Clone config from active profile
         </label>
+        <input id="profileFormBaseUrl" placeholder="Base URL (optional, e.g. http://localhost:11434)" style="width:100%;background:rgba(255,255,255,.05);border:1px solid var(--border2);border-radius:6px;color:var(--text);padding:5px 8px;font-size:12px;outline:none;margin-bottom:6px;box-sizing:border-box">
+        <input id="profileFormApiKey" type="password" placeholder="API key (optional)" style="width:100%;background:rgba(255,255,255,.05);border:1px solid var(--border2);border-radius:6px;color:var(--text);padding:5px 8px;font-size:12px;outline:none;margin-bottom:6px;box-sizing:border-box">
         <div style="display:flex;gap:6px">
           <button class="cron-btn run" style="flex:1" onclick="submitProfileCreate()">Create</button>
           <button class="cron-btn" style="flex:1" onclick="toggleProfileForm()">Cancel</button>