Replace bundled ROM extraction with runtime import/download flow

Commodore ROMs are copyrighted and can no longer ship inside the APK.
MainActivity now detects missing ROMs on first launch and blocks
startup with a dialog offering two paths: pick files via the system
file picker, or download the official VICE 3.8 tarball and extract the
four ROMs from it client-side (minimal USTAR reader, no extra deps).

- Drop the extractViceRoms Gradle task and asset bundling; add
  res/extract_roms.sh for local sideloading during development instead
- gitignore keystores/keystore.properties ahead of a signed release
- Move architecture.md into docs/, refresh it for the screen-mirroring
  and watch-input additions, and add accompanying Mermaid diagrams
- Add docs/debugging.md and docs/publish.md (Play Store release notes,
  ROM-import compliance rationale)

SchwertUndMagieOnPebbleCompanionApp/res/extract_roms.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# Extracts the C64 and 1541 ROMs needed by vice_jni.c from vice-3.8.tar.gz.
+#
+# This is a manual/standalone equivalent of the `extractViceRoms` Gradle task
+# in app/build.gradle.kts — same source paths, same renaming. Useful for
+# inspecting the ROMs outside a full Gradle build (e.g. for the "bring your
+# own ROM" flow described in docs/publish.md §0).
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+TARBALL="$SCRIPT_DIR/vice-3.8.tar.gz"
+DEST="${1:-$SCRIPT_DIR/roms}"
+
+if [[ ! -f "$TARBALL" ]]; then
+    echo "error: $TARBALL not found" >&2
+    exit 1
+fi
+
+mkdir -p "$DEST"
+WORK_DIR="$(mktemp -d)"
+trap 'rm -rf "$WORK_DIR"' EXIT
+
+tar -xzf "$TARBALL" -C "$WORK_DIR" \
+    vice-3.8/data/C64/kernal-901227-03.bin \
+    vice-3.8/data/C64/basic-901226-01.bin \
+    vice-3.8/data/C64/chargen-901225-01.bin \
+    "vice-3.8/data/DRIVES/dos1541-325302-01+901229-05.bin"
+
+cp "$WORK_DIR/vice-3.8/data/C64/kernal-901227-03.bin"            "$DEST/kernal"
+cp "$WORK_DIR/vice-3.8/data/C64/basic-901226-01.bin"             "$DEST/basic"
+cp "$WORK_DIR/vice-3.8/data/C64/chargen-901225-01.bin"           "$DEST/chargen"
+cp "$WORK_DIR/vice-3.8/data/DRIVES/dos1541-325302-01+901229-05.bin" "$DEST/1541"
+
+echo "Extracted kernal, basic, chargen, 1541 to $DEST"