docs: add CMUcam legacy section (CMUcam1-5)

Preserve the CMUcam project (cmucam.org, now offline) as a Legacy section in
the docs, scraped from the Wayback Machine. Adds an intro page plus per-camera
sections for CMUcam1-4 (overview, wiki, and sub-pages, with downloads and
converted-to-MP4 videos) and a Pixy (CMUcam5) landing page pointing at the live
pixycam.com. External links point at their real online destinations, not the
archive. Linked after License in the toctree; excluded from the offline/IDE
bundle via the parent repo's snapshot pruning.

CMUcam4 and CMUcam5 are still being finished; CMUcam3 may remain partial for a
while.

A scoped docs/legacy/.gitattributes forces the archive's binary asset types
(.bmp/.zip/.ppt/.tar and uppercase image/pdf extensions) to binary, since the
repo-wide `* text eol=lf` would otherwise corrupt them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: kwagyeman

docs/index.rst

@@ -13,3 +13,4 @@ OpenMV MicroPython documentation
     Internals <develop/index.rst>
     Changelog <changelog/index.rst>
     License <license.rst>
+    Legacy <legacy/index.rst>

docs/legacy/.gitattributes

@@ -0,0 +1,24 @@
+# The repo root sets `* text eol=lf`, which would corrupt binary assets that
+# are not on its whitelist (and its patterns are lowercase / case-sensitive).
+# The legacy CMUcam archive carries several such types, so force them binary
+# here in both cases.
+*.bmp binary
+*.BMP binary
+*.zip binary
+*.ZIP binary
+*.ppt binary
+*.PPT binary
+*.tar binary
+*.TAR binary
+*.jpg binary
+*.JPG binary
+*.jpeg binary
+*.JPEG binary
+*.png binary
+*.PNG binary
+*.pdf binary
+*.PDF binary
+*.gif binary
+*.GIF binary
+*.mp4 binary
+*.MP4 binary