SPEC v0.1 and project rules for Kvitt

Write SPEC.md v0.1 from the owner interview (requirements, data model,
stack, API outline, security, business rules, deployment, milestones,
UX sprint brief, contracts). Fill the CLAUDE.md blanks, move the Gradle
pin files into android/, point the tools at android/ and server/, and
record the git bootstrap exception in the handoff.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -16,3 +16,14 @@ export/
 .claude/worktrees/
 # macOS
 .DS_Store
+# Rust build output
+target/
+# Server data, keys and certificates (they live on the Pi or in infra/secrets/, never in git)
+infra/secrets/
+*.sqlite
+*.sqlite3
+*.db
+*.pem
+*service-account*.json
+google-services.json
+*.apk