docs: release notes for v2.11.1

Plain-English notes for the Windows file-handle fix:
- RELEASE_NOTES.md is the override the GitHub Actions release
  workflow injects into the GitHub Release body
- README.md gets the matching entry in the Release Notes section
  so repo visitors see the v2.11.1 fix in context

Tone is teacher-friendly: explains what they would have noticed
(can't open template in Adobe, can't rename in Explorer, etc.)
rather than "PdfReader file handle leak."

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mrdavearms

README.md

@@ -818,6 +818,15 @@ bulk-pdf-extractor-and-generator/
 
 ## Release Notes
 
+### v2.11.1 — May 2026
+
+**Small reliability fix.** Patch release — no new features, no changes to how you use the app. Safe to upgrade at any time.
+
+- **Fixed: template PDF stayed "in use" by the app on Windows after Load Data** — On the **Generate PDFs** tab, after clicking **Load Data**, Windows could keep treating your template PDF as "open by another program". You may have noticed this if you tried to open the same template in Adobe Acrobat (got a "file in use" warning), rename or move the template in File Explorer (blocked), run a second copy of the app on the same template, or email/upload the template while the app was still open. The file is now released back to Windows as soon as the app finishes reading the form fields. macOS users were not affected.
+- **Behind the scenes** — internal architecture documentation has been brought up to date with the threading and caching improvements that landed in v2.11. No user-facing change.
+
+---
+
 ### v2.11 — April 2026
 
 **Reliability, performance, and stability fixes** — full codebase audit pass.

RELEASE_NOTES.md

@@ -1,3 +1,17 @@
+**Small reliability fix.** This is a patch release with one targeted fix — no new features and no changes to how you use the app. Safe to upgrade at any time.
+
+- **Fixed: template PDF stayed "in use" by the app on Windows after Load Data** — On the **Generate PDFs** tab, after you clicked **Load Data**, Windows could keep treating your template PDF as "open by another program" — even though you were just using it as a source for field names. You may have noticed this if you tried to:
+  - Open the same template in Adobe Acrobat or Adobe Reader and got a "file in use" warning,
+  - Rename, move, or delete the template in File Explorer and got blocked by Windows,
+  - Run a second copy of the app on the same template,
+  - Email or upload the template while the app was still open.
+
+  The file is now released back to Windows as soon as the app finishes reading the form fields, so all of the above just work normally. **macOS users were not affected** — macOS handles open file handles differently and never blocked these operations.
+
+- **Behind the scenes** — the app's internal architecture documentation has been brought up to date with the threading and caching improvements that landed in v2.11. No user-facing change.
+
+---
+
 <!-- Release notes for the next tagged release.
      The GitHub Actions workflow reads this file and injects it into the
      release page. Write in plain English for teachers — no jargon.