docs: v2.16.3 technical release notes

[mohnjiles]

Summary

Adds the missing docs/release-notes/2.16.3.md page — the extended technical notes for the v2.16.3 release, following the same format as the existing 2.16.2 page (intro pointing at the CHANGELOG for the user-facing summary, table of contents, then a deeper how-and-why section per change).

Sections

• CivitAI Workflow Browsing (headline feature, most depth: browsing/importing, PNG-embedded workflow imports, custom node install assist, ComfyUI library linking, preview sizing)
• In-App Documentation (shipped in 2.16.2, recorded retroactively)
• CivArchive browser after the site redesign (search route pinning, renamed API fields, redirect handling, preview backfill)
• Model update checks (Checkpoint manager Bug that needs either Fixing or improving or overhauling etc #1716 phantom badges, multi-architecture comparisons, early-access deadline field)
• Model index case-conflicting folders (Still crashing when conflicting folders exist. #1715)
• Model browser fixes (Hash signs (#) in File Name Pattern break model cover/preview display in Model Manager #1703, Model browser items display in wrong order after actively clicking the "Search" button #1705, Some downloads incorrectly fetch other model files within the same version, causing hash verification failures #1710)
• Extension install/detection fixes (Inference telling me to install gguf plugin which already exists #1717, legacy source builds, Error when using the Layer Diffuse (SDXL) option #1707 Layer Diffuse)
• Python/uv/package environments (uv 0.12.5 / Python 3.10.20 is the latest safe version of Python 3.10 #1709, Can't install Stable Diffusion - Neo on Linux. #1713, Python fallback matching, pyvenv.cfg rewriting, package-env breakage)
• Trainer and platform fixes (AI-Toolkit PyTorch 2.13.0 / Update antiqated pytorch for AI-Toolkit #1714, OneTrainer Windows-ROCm profile installs bitsandbytes 0.50.0.dev0, which OneTrainer doesn't support yet — bnb 8-bit optimizers crash #1708, SwarmUI launch mode, Clear Finished)

All facts are drawn from CHANGELOG.md and the release's commits; anything not derivable from those sources was left out.

Suggestion

The docs site's latest release-notes page currently lags the CHANGELOG whenever a release ships without its page (as happened here for 2.16.3). It might be worth adding a short release checklist item — e.g. a step in the release process reminding to write/publish the matching docs/release-notes/<version>.md — so future releases don't repeat this gap. Happy to help with that separately if there's interest.

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[mohnjiles]

Closing in favor of a fresh branch — the commit message on this one referenced the internal origin of the change; reopening a clean PR with the same content.