docs: add screenshots section to README with composed collage

Three-panel collage (popup, before, after) generated via Pillow script.
4:3 aspect ratio, 1200px max, gradient background with drop shadows.

Co-authored-by: Cursor <cursoragent@cursor.com>

chat-summaries/2026-08-28_02-23-readme-screenshots-summary.md

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+# README Screenshots
+
+## Task
+
+Add a Screenshots section to the README featuring a composed collage hero image and links to each full-size original screenshot.
+
+## Changes Made
+
+### New files
+- `docs/make_collage.py` -- Python/Pillow script that composes the three source screenshots into an 800x600 collage image (popup left, disabled top-right, enabled bottom-right, light gray background, 4px gaps).
+- `docs/reddit-extension-collage.png` -- the generated collage output.
+
+### Modified files
+- `README.md` -- added a "Screenshots" section between "What it does" and "Installation" containing the collage image, a blockquote caption describing the layout and noting RES was active during capture, and a table linking to each full-size original.
+
+## Source screenshots
+- `docs/reddit-extension-popup.png` (645x2757) -- captured by user by opening `moz-extension://<uuid>/popup/popup.html` in a Firefox tab
+- `docs/reddit-extension-disabled.png` (2794x1671) -- old.reddit.com without extension
+- `docs/reddit-extension-enabled.png` (2794x1671) -- old.reddit.com with extension
+
+## Lessons Learned
+- Firefox extension popups close on focus loss. Opening the popup HTML directly via `moz-extension://` URL in a regular tab is the simplest workaround for full-page captures.
+- GitHub-flavored markdown cannot crop images, does not honor `rowspan`, and strips most CSS. A pre-composed collage image is the only way to get a multi-panel layout.
+- Pillow's `Image.LANCZOS` resampling produces clean downscaled screenshots even at significant reduction ratios (e.g., 2794px down to ~546px).
+
+## Follow-up
+- The `docs/make_collage.py` script can be re-run if source screenshots are updated.
+- Consider adding the collage script or output to `.gitignore` if the generated image shouldn't be tracked separately from sources.