fix: agent_run param mismatch (send agent_name) + add GitHub push-update (3 inputs: repo name, token, username; --force-with-lease)

Fixes agent_run + adds GitHub push-update:

FIX: handle_agent_run param mismatch
- Backend declared 8 params (prompt, target_language, target_framework,
history_json, skills_json, search_enabled, image_url, agent_name)
but frontend POST body only sent 7 — Gradio raised
'needed: 8, got: 7'. Frontend now sends state.activeAgent as the
8th value, restoring agent_run for ALL prompts (the bug broke agent
mode entirely after the Custom Agents feature shipped).

FEAT: Push Update to GitHub (3 inputs only)
- New backend: code/tools/github.py::push_to_github(repo_name,
github_token, username, branch?, commit_message?, timeout?)
- Workflow: snapshot workspace → fresh git repo in temp dir →
git add -A + git commit → git push --force-with-lease
https://<user>:<token>@github.com/<owner>/<repo>.git <branch>.
- Falls back to plain push if --force-with-lease fails on a brand-new
empty repo (no refs to lease against).
- Token is scrubbed from error messages before being returned.
- New API: push_github(repo_name, github_token, username, ...)
- New UI: 'Push Update to GitHub' section in the Deploy tab with 3
required inputs (repo name, GitHub token, username) + an Advanced
<details> for branch/commit_message.
- Updated README.md and CLAUDE.md with new feature docs.

index.html

@@ -675,9 +675,11 @@ body.hide-thinking .think-block { display: none; }
 /* Agent tab — scrollable like the Deploy tab.
    Override .tab-pane.active's `display:flex` so the single .deploy-section
    child does not get squished by flex shrink, which was preventing the
-   pane from scrolling. */
+   pane from scrolling.
+   NOTE: `display:none` is inherited from `.tab-pane` (base); only the
+   `.active` state flips to `display:block`. Don't put `display:block` on
+   the base `#pane-agent` or both panes will render at the same time. */
 #pane-agent {
-  display: block !important;
   padding: 16px;
   overflow-y: auto;
   overflow-x: hidden;
@@ -871,7 +873,6 @@ body.hide-thinking .think-block { display: none; }
    DEPLOY TAB
    ═══════════════════════════════════════════════════════ */
 #pane-deploy {
-  display: block !important;
   padding: 16px;
   overflow-y: auto;
   overflow-x: hidden;