chore: Tier-1 storage optimization (LFS doc images + gc) (#1768)

Follow-up to #1767. Safe, track-forward storage cleanup — **no history
rewrite, no force-push.**

## What
- Extend the Git LFS policy from GIFs to **documentation/marketing PNG
screenshots** (`docs/screenshots/**`, `demo/**`, top-level
`screenshots/**`) — 53 PNGs converted to LFS pointers.
- Ran `git gc --prune=now` locally: consolidated 7 packfiles → 1 and
pruned loose objects (**local `.git` 421M → 300M**; this is a
local-clone benefit, not a remote-history change).

## Deliberately excluded (stay as real blobs)
These are build/runtime assets — an LFS-less build env would otherwise
embed a 132-byte pointer stub and break them:
- `packages/dashboard/app/public/icons/*.png` — PWA manifest icons
(served)
- `packages/desktop/src/icons/*.png` — Electron app/tray icons
(packaged)
- `packages/dashboard/app/public/fonts/SymbolsNerdFontMono-Regular.ttf`
— `@font-face` source (served)

## Verified
- No runtime icon/font asset entered LFS (`git lfs ls-files` excludes
`icons/`, `fonts/`, `.ttf`).
- `docs-screenshot-links` test still passes — it checks path existence,
and LFS pointer files satisfy `existsSync`.

## Not in scope
The ~300MB of stale binary history (old GIF/PNG revisions) is only
reclaimable via a history rewrite (force-push + re-clone) — tracked
separately as Tier 2.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Workflow editing now opens in a floating window with improved drag,
sizing, and close behavior.
* Workflow switchers now pass the selected workflow into the editor, so
the chosen workflow opens directly.

* **Bug Fixes**
* Improved mobile and desktop layout behavior for the workflow editor,
including overlay sizing and scroll handling.
* Updated navigation and onboarding flows to match the latest sidebar
and empty-state behavior.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.gitattributes

@@ -4,3 +4,15 @@
 # live outside the packfile and future regenerations stop bloating .git.
 # Scoped to demo/assets/*.gif (track-forward only — existing history was left intact).
 demo/assets/*.gif filter=lfs diff=lfs merge=lfs -text
+
+# FNXC:RepoAssets 2026-06-25-09:40:
+# Documentation/marketing PNG screenshots are pure doc assets (referenced only from
+# markdown, rendered by GitHub) so they are safe to route through LFS alongside the GIFs.
+# IMPORTANT: scope to doc/demo dirs ONLY. App-runtime/build images must stay as real
+# blobs because a build env without LFS hydration would otherwise embed a pointer stub:
+#   - packages/dashboard/app/public/icons/*.png  (PWA manifest icons, served)
+#   - packages/desktop/src/icons/*.png            (Electron app/tray icons, packaged)
+#   - packages/dashboard/app/public/fonts/SymbolsNerdFontMono-Regular.ttf (@font-face src)
+demo/**/*.png filter=lfs diff=lfs merge=lfs -text
+docs/screenshots/**/*.png filter=lfs diff=lfs merge=lfs -text
+screenshots/**/*.png filter=lfs diff=lfs merge=lfs -text