Sync dev to main: broken link fixes - #1097

Checked all 513 external URLs in the docs. Most failures were noise:
printables.com 403s under bot protection even with a browser user agent,
SmartThings API endpoints in code examples, and local addresses like
192.168.1.1 that cannot resolve from here. What remained splits in two.

Three internal links were broken. The BTN-1 getting started page pointed
at a blueprint page slug that does not exist, the correct page is
btn1/examples/blueprint. A homey battery page sent readers to
plt1/setup/general-tips, which is not a path on this wiki and does not
describe a boot button either; it now points at plt1-boot-mode, matching
the sibling link two lines above it in the same file. The R-PRO-1 code
page carried a .md suffix inside an absolute URL, so the page it wanted
was there all along.

The rest pointed at apolloautomation.github.io, the retired GitHub Pages
wiki. Six of those were images hotlinked into the two PLT-1B factory
reflash pages, all returning 404, so readers following that guide saw
three missing screenshots at the steps that need them most. The same
three files already sit in docs/assets under identical names, so the
images become local paths. The remaining links were live but still sent
readers to the old wiki, so they now point at the equivalent page here.
Homey pages point at homey pages.

The TEMP-PRO-1 boot mode page linked the TEMP-1 upload guide and carried
a literal "(needs new link)" in the published text. temp-pro1-code exists,
so the link goes there and the marker is gone.

Verified every replacement target returns 200 and every referenced asset
exists in the repo. No apolloautomation.github.io/docs reference remains.

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