feat: add post3 s3 proxy for postgresql

Signed-off-by: kjuulh <contact@kjuulh.io>

todos/POST3-001-workspace-skeleton.md

@@ -0,0 +1,21 @@
+# POST3-001: Create workspace skeleton
+
+**Status:** Done
+**Priority:** P0
+**Blocked by:** —
+
+## Description
+
+Set up the Rust workspace with both crates, Docker Compose for PostgreSQL 18, and mise.toml dev tasks.
+
+## Acceptance Criteria
+
+- [ ] `Cargo.toml` workspace root with `crates/*` members
+- [ ] `crates/post3/Cargo.toml` — library crate with sqlx, tokio, bytes, chrono, md-5, hex, thiserror, uuid, tracing, serde
+- [ ] `crates/post3/src/lib.rs` — empty module declarations
+- [ ] `crates/post3-server/Cargo.toml` — binary crate depending on post3, axum, clap, notmad, quick-xml, etc.
+- [ ] `crates/post3-server/src/main.rs` — minimal tokio main
+- [ ] `templates/docker-compose.yaml` — PostgreSQL 18 on port 5435
+- [ ] `mise.toml` — tasks: up, down, dev, test, db:shell, db:migrate
+- [ ] `cargo check --workspace` passes
+- [ ] `mise run up` starts PostgreSQL successfully