scripts: add portable packaging helpers for Windows and Linux (T7.1-T7.2)

package-windows.bat builds gosentry.exe then bundles it with README and
CHANGELOG into a versioned .zip via PowerShell Compress-Archive.
package-linux.sh does the same for linux-amd64 and linux-arm64 (arm64
cross-compiles via aarch64-linux-gnu-gcc; skips gracefully if absent),
producing .tar.gz archives with files at the archive root.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/RELEASE-0.10-TASKS.md

@@ -118,8 +118,8 @@ Done first because both share a compact, single-line record formatter.
 - [x] T6.4 — ARCHITECTURE.md update
 
 ### Phase 7 — Portable packaging
-- [ ] T7.1 — Windows `.zip`
-- [ ] T7.2 — Linux `.tar.gz` (amd64 + arm64)
+- [x] T7.1 — Windows `.zip`
+- [x] T7.2 — Linux `.tar.gz` (amd64 + arm64)
 
 ### Phase 8 — Release docs + version
 - [ ] T8.1 — version bump + CHANGELOG + ROADMAP + PERFORMANCE