feat(skills): import SKILL.md bundles from public GitHub URLs (#2576)

* feat(skills): import SKILL.md bundles from public GitHub URLs

Supports GitHub tree/blob/raw links and skills.sh pages that resolve to GitHub.
Installs SKILL.md plus sibling text assets under data/skills/imported/.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): admin-gate URL import and validate redirect hosts

- require_admin on POST /api/skills/import-from-url (matches other skill admin routes)
- reject cross-host redirects after httpx follow_redirects
- test for redirect host validation

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): match Brain Add panel import/submit button styles

- Skill URL Import: theme-io-btn + download icon (same as memory Import)
- Add Skill submit: confirm-btn confirm-btn-primary

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): allow api.github.com during directory import

Real imports hit the GitHub contents API after redirects; whitelist
api.github.com and add regression tests. Shrink Import button with flex:none.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): align skill Import button with URL input row

Match memory-add-input height (28px) in memory-add-row and center the
download icon with flexbox instead of vertical-align hacks.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): cancel modal-body margin on skill Import button

The skill Import button sits in .memory-add-row beside an input; the
global .modal-body button { margin-top: 6px } rule only affected buttons,
pushing Import down and misaligning the download icon. Reset margin-top
and match Memory Import SVG markup at 28px row height.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(skills): surface GitHub API errors on URL import

Pass through GitHub response messages (especially 403 rate limits) as
SkillImportError instead of a generic download failure.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

static/index.html

@@ -314,7 +314,15 @@
             <div style="display:flex;align-items:baseline;gap:8px;margin-bottom:2px;">
               <h2 style="margin:0;padding:0;line-height:1;"><svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" style="vertical-align:-2px;margin-right:6px"><polygon points="13 2 3 14 12 14 11 22 21 10 12 10 13 2"/></svg>Add Skill</h2>
             </div>
-            <p class="memory-desc doclib-desc" style="margin-top:6px;">Create a skill by hand — title, what it solves, and an approach.</p>
+            <p class="memory-desc doclib-desc" style="margin-top:6px;">Import a skill from GitHub or <a href="https://skills.sh" target="_blank" rel="noopener noreferrer">skills.sh</a> (folder with <code>SKILL.md</code> and optional templates).</p>
+            <div class="memory-add-row" style="margin-top:6px;margin-bottom:10px;">
+              <div class="skill-ph-wrap" style="flex:1;min-width:0;">
+                <input type="url" id="skill-import-url" placeholder=" " class="memory-add-input skill-hint-input" aria-label="Skill import URL" />
+                <span class="skill-rich-ph"><span class="k">Import URL</span> — e.g. GitHub tree link to a skill folder</span>
+              </div>
+              <button type="button" id="skill-import-url-btn" class="theme-io-btn" title="Import skill from URL" style="flex:none;height:28px;font-size:12px;"><svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" style="vertical-align:-2px;margin-right:4px;" aria-hidden="true"><path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4"/><polyline points="7 10 12 15 17 10"/><line x1="12" y1="15" x2="12" y2="3"/></svg>Import</button>
+            </div>
+            <p class="memory-desc doclib-desc" style="margin-top:0;">Or create a skill by hand — title, what it solves, and an approach.</p>
             <div class="skill-ph-wrap" style="margin-top:4px;margin-bottom:6px;">
               <input type="text" id="new-skill-title" placeholder=" " class="memory-add-input skill-hint-input" aria-label="Skill title" />
               <span class="skill-rich-ph"><span class="k">Title</span> — short name, e.g. “build-vllm-wheel”</span>
@@ -332,7 +340,7 @@
               <span class="skill-rich-ph"><span class="k">Tags</span> — comma-separated, e.g. python, build, vllm</span>
             </div>
             <div style="display:flex;justify-content:flex-end;">
-              <button id="add-skill-btn" class="memory-toolbar-btn">Add Skill</button>
+              <button id="add-skill-btn" class="confirm-btn confirm-btn-primary">Add Skill</button>
             </div>
           </div>
         </div>