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/landing.rs

@@ -0,0 +1,26 @@
+//! E-4 invite landing page (AC-2.5).
+//!
+//! Registered and annotated by M2a; M3 owns this file and implements the handlers (until then 501
+//! `not_implemented`).
+
+use crate::api::not_implemented;
+use crate::error::AppError;
+
+#[utoipa::path(
+    get,
+    path = "/i/{code}",
+    operation_id = "getInviteLanding",
+    summary = "E-4 Invite landing page (HTML)",
+    description = "HTML per AC-2.5 for any `code` of 1 to 32 characters; validity is not checked. Swedish when `Accept-Language` prefers `sv`, English otherwise.",
+    security(()),
+    params(
+        ("code" = String, Path),
+    ),
+    responses(
+        (status = 200, description = "Landing page.", body = String, content_type = "text/html; charset=utf-8"),
+        (status = 404, description = "`code` not 1 to 32 characters: an HTML 404 page.", body = String, content_type = "text/html; charset=utf-8"),
+    )
+)]
+pub async fn get_invite_landing() -> AppError {
+    not_implemented()
+}