chore: take theme v3.0.0, migrating the launch and footer config

v3.0.0 is a breaking release for this repo's config: the five `launch_*`
options are replaced, and a site that bumps the pinned theme without
editing `myst.yml` silently loses its Launch control.

The launch values are ported from the Sphinx build rather than invented --
`nb_repository_url` becomes `launch_notebook_repo` and `path_to_docs`
becomes `launch_notebook_source_dir`, with `launch_colab: true` standing in
for the `launch_buttons.colab_url` entry. The branch is left unset because
`main` is the default. Nothing is derived from `project.github` any more,
so the comment above it that said otherwise is corrected.

`site.parts.footer` and `lectures/footer.md` are removed: the theme renders
the licence notice by default from v3.0.0, and declaring a footer part
replaces that whole block. The default is a superset of what the file had
-- it adds the "A theme by QuantEcon" credit the Sphinx sites carried, which
footer.md had dropped. `lectures/_static/ccbysa.png` goes with it, since the
badge is now an inline SVG in the theme and nothing else referenced it.

`site_url` comes from the Sphinx build's `html.baseurl` and is what makes
the theme emit a canonical link and `og:url`.

`need_for_speed.md` and `polars.md` lose their `{raw} jupyter`
notebook-header blocks, rewritten out by the theme repo's
`scripts/rewrite-raw-blocks.mjs`: mystmd renders no `raw` node, so each
block's own source was reaching readers as escaped text under the page
title.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: mmcky

lectures/_static/ccbysa.png

@@ -13,8 +13,9 @@ project:
         - Instructor for Ph.D. Advanced Macroeconomics, University of Minnesota.
       url: https://johnstachurski.net
       email: john.stachurski@gmail.com
-  # The theme derives the notebook-launch repo from this (github + ".notebooks"),
-  # so it has to be the real repo name.
+  # Commit and "edit this page" links target this repo. The notebook-launch
+  # repository is no longer derived from it: from theme v3.0.0 it is named
+  # explicitly by `launch_notebook_repo` under `site.options`.
   github: https://github.com/QuantEcon/lecture-python-programming
   # Keep in sync with _toc.yml (the jupyter-book 1.x table of contents).
   toc:
@@ -88,9 +89,23 @@ project:
   #   - id: book-pdf
   #     title: Book (PDF)
 site:
-  parts:
-    footer: footer.md
+  # No `parts.footer`: from theme v3.0.0 the licence notice and the QuantEcon
+  # credit are rendered by default, and declaring a footer part replaces that
+  # whole block. Only a site under other terms supplies one.
+  #
   # Pinned theme release (see https://github.com/QuantEcon/quantecon-theme.mystmd/releases);
   # bump the vX.Y.Z in this URL to take a new theme version. The old bundled
   # QuantEcon/quantecon-theme repo is archived.
-  template: https://github.com/QuantEcon/quantecon-theme.mystmd/releases/download/v2.7.0/quantecon-theme.zip
+  template: https://github.com/QuantEcon/quantecon-theme.mystmd/releases/download/v3.0.0/quantecon-theme.zip
+  options:
+    # The site's public URL, which the theme needs for the canonical link,
+    # og:url and an absolute og:image. Carried over from the Sphinx build's
+    # `html.baseurl`.
+    site_url: https://python-programming.quantecon.org/
+    # Launch is opt-in from theme v3.0.0: the notebook repository is named
+    # here rather than derived from `project.github`. These two carry over
+    # from the Sphinx build's `nb_repository_url` and `path_to_docs`; the
+    # branch defaults to `main`, so it is left unset.
+    launch_notebook_repo: QuantEcon/lecture-python-programming.notebooks
+    launch_notebook_source_dir: lectures
+    launch_colab: true

lectures/footer.md

@@ -10,14 +10,6 @@ kernelspec:
 ---
 
 (speed)=
-```{raw} jupyter
-<div id="qe-notebook-header" align="right" style="text-align:right;">
-        <a href="https://quantecon.org/" title="quantecon.org">
-                <img style="width:250px;display:inline;" width="250px" src="https://assets.quantecon.org/img/qe-menubar-logo.svg" alt="QuantEcon">
-        </a>
-</div>
-```
-
 # Python for Scientific Computing
 
 ```{epigraph}

lectures/myst.yml

@@ -12,14 +12,6 @@ kernelspec:
 ---
 
 (pl)=
-```{raw} jupyter
-<div id="qe-notebook-header" align="right" style="text-align:right;">
-        <a href="https://quantecon.org/" title="quantecon.org">
-                <img style="width:250px;display:inline;" width="250px" src="https://assets.quantecon.org/img/qe-menubar-logo.svg" alt="QuantEcon">
-        </a>
-</div>
-```
-
 # Polars
 
 ```{index} single: Python; Polars