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/proposal.rs

@@ -0,0 +1,28 @@
+//! E-33 settlement allocation proposal (SPEC §9.4).
+//!
+//! 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::auth::AuthDevice;
+use crate::error::AppError;
+use crate::openapi::responses::{BadRequest, Conflict, Unprocessable};
+use crate::wire::{ProposalRequest, ProposalResponse};
+
+#[utoipa::path(
+    post,
+    path = "/settlements/proposal",
+    operation_id = "proposeSettlement",
+    summary = "E-33 Server-side allocation proposal",
+    description = "Computed with `kvitt-domain::propose_allocation` (SPEC §9.4) over the server's non-deleted rows.",
+    request_body(content = ProposalRequest, content_type = "application/json; charset=utf-8"),
+    responses(
+        (status = 200, description = "The proposal.", body = ProposalResponse, content_type = "application/json; charset=utf-8"),
+        (status = 400, response = BadRequest),
+        (status = 409, response = Conflict),
+        (status = 422, response = Unprocessable),
+    )
+)]
+pub async fn propose_settlement(_device: AuthDevice) -> AppError {
+    not_implemented()
+}