fix(web): serve the Predbat logo locally instead of from GitHub

[chalfontchubby]

Summary

• The dashboard's favicon and header logo were fetched from raw.githubusercontent.com on every page load; a GitHub outage or 429 rate limit left every page hanging for ~15s before it would render (Predbat Dash doesn't render until bat_logo_light.png logo downloads or fails #4562).
• The logo images now ship alongside the app (apps/predbat/bat_logo*.{svg,png}, same as the existing .so kernel binaries) and are served from a new local /images/{filename} route, whitelisted to just those three files.
• docs/images/bat_logo* were removed rather than duplicated - nothing else in the repo referenced them, so there's a single canonical copy with no drift risk.

Fixes #4562

Test plan

• New web_logo_image unit test: route serves each logo with the right content type, 404s for anything not on the whitelist, and the page header no longer references githubusercontent.com
• ./run_all --test web_logo_image --test web_functions --test web_annual_routes_registered passes
• ./run_pre_commit passes (black, ruff, cspell, etc.)

🤖 Generated with Claude Code

[springfall2008]

Good idea @chalfontchubby but the downloader will need updating to include the images

[chalfontchubby]

And that needs to be merged/installed before we can use it in the version it downloads. Same as the "wb" issue on the .so files.

[chalfontchubby]

I'll fail safe if the image isn't in the apps dir.

[springfall2008]

And that needs to be merged/installed before we can use it in the version it downloads. Same as the "wb" issue on the .so files.

Yes, suggest adding the installer update in the same PR, the fallback should be fine until its rolled out

[chalfontchubby]

I believe so long as 8ab260b — about 8 months old - is there, you don't have a manifest - the svg files are in a dir that should be autodetected and no change is needed to the downloader.... (?)