PIPE-2738P Migrate releases/timeline to MyST Markdown
Convert releases.rst and timeline.rst to MyST-compatible
Markdown (.md). Both files used RST-only syntax (.. mermaid::,
.. contents::, :field:, .. note::) that is now replaced with
fenced directives, definition lists, and standard Markdown links.
- releases: 6-column list-table reduced to 5 columns by merging
Documentation + Download into a single Resources column; download
link text shortened to "Download (linux/macOS)"; :widths: auto added
- timeline: .. mermaid:: blocks converted to ```{mermaid}```; gitGraph
YAML front-matter replaced with %%{init:…}%% inline config; RST
field lists converted to deflist syntax; .. note:: → ```{note}```
- timeline moved from Basics to Misc. section in index.rst
- Add autosummary base.rst template so generated stubs use short
names (objname) instead of full dotted paths (fullname)
- Reduce global font size to ~13px via :root { font-size: 81.25% }
in custom_theme.css so all rem-based Furo sizes scale uniformly
