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>

tools/install-git-hooks.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 # Installs the Kvitt pre-commit hook into this repository's hooks folder (shared by all worktrees).
-# The hook guards itself: on branches without the app build it only runs the export/ check.
+# The hook guards itself: on branches without android/ or server/ it only runs the secrets check.
 set -euo pipefail
 here="$(cd "$(dirname "$0")" && pwd)"
 hooks="$(git -C "$here" rev-parse --path-format=absolute --git-common-dir)/hooks"