M2a: server workspace, kvitt-domain, skeleton routes, OpenAPI match, Dockerfile

Cargo workspace (kvitt-domain, kvitt-server, kvitt-import), Rust 1.99.1 pinned.
kvitt-domain passes every Rust vector and adds next_occurrence_date (D-015).
kvitt-server: config, SQLite pool (WAL, §8.9 pragmas), migration 0001 identical to
the contract schema, error type for all 25 codes, auth extractor and protocol
layer, all 33 routes (E-1/E-2 implemented, the rest 501), utoipa document equal
to contracts/openapi.yaml, seams for M3/M4/M9, serve/migrate/healthcheck.

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

server/crates/kvitt-server/src/api/rate_limit.rs

@@ -0,0 +1,8 @@
+//! Rate limiting (SPEC §8.6). M3 owns this file; in M2a the layer lets every request through.
+
+use tower::layer::util::Identity;
+
+/// The rate-limit layer `router.rs` attaches to every route.
+pub fn layer() -> Identity {
+    Identity::new()
+}