[AZ-640] Bootstrap Rust workspace, CI/Docker, observability scaffold

Lands the first task of the implementation epic AZ-626: a cargo workspace
with 14 crates (shared + autopilot binary + 12 component crates), a
multi-stage Dockerfile + dev/test compose stacks, a Woodpecker CI pipeline,
the on-airframe systemd unit with flight-gate wiring, three environment
TOML configs, and the canonical entity catalogue from data_model.md as
`shared::models`.

Per-AC verification (full detail in
_docs/03_implementation/batch_01_cycle1_report.md):

- AC-1 cargo check --workspace clean
- AC-2 cargo test --workspace passes; per-crate it_compiles() <0.01 s
- AC-6 cargo build/test --no-default-features clean; VlmClient default
       impl returns VlmAssessment::disabled()
- AC-9 tracing-subscriber emits JSON logs with ts/level/target/fields
- AC-10 runtime::ensure_state_directories creates mapobjects/, audit/,
        pending_pushes/ under storage.state_dir

Deferred to external infra (artifacts written, verification re-runs in CI
and in downstream tasks):
- AC-3 Woodpecker runner; CI yml in place
- AC-4 docker-compose mocks land with AZ-660/AZ-644/AZ-675
- AC-5 SITL conformance lands with AZ-641/AZ-648/AZ-652
- AC-7 aarch64 cross-compile via cargo-zigbuild stage
- AC-8 systemd unit (Linux + systemd host)

Layering invariants from module-layout.md hold: shared (L1) imports
nothing; Layer 2 actor crates import only shared; Layer 3 coordinators
(operator_bridge, mission_executor) import only their documented Layer 2
deps; Layer 4 (scan_controller) imports its documented Layer 2 + Layer 3
deps; the autopilot binary (L5) is the only consumer of every component.

cargo fmt --all --check + cargo clippy --all-targets -- -D warnings both
clean. Jira AZ-640 transitioned to In Progress at the start of this batch;
the matching In Testing transition follows this commit.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/mavlink_layer/src/lib.rs

@@ -0,0 +1,80 @@
+//! `mavlink_layer` — hand-rolled MAVLink v2 transport.
+//!
+//! Real implementation lands in:
+//! - AZ-641 `mavlink_transport_and_heartbeat`
+//! - AZ-642 `mavlink_codec`
+//! - AZ-643 `mavlink_ack_demux_and_signing`
+
+use async_trait::async_trait;
+
+use shared::contracts::MavlinkSink;
+use shared::error::{AutopilotError, Result};
+use shared::health::ComponentHealth;
+
+const NAME: &str = "mavlink_layer";
+
+#[derive(Debug, Clone)]
+pub struct MavlinkConnection {
+    pub uri: String,
+}
+
+#[derive(Debug, Clone)]
+pub struct MavlinkLayer {
+    connection: MavlinkConnection,
+}
+
+impl MavlinkLayer {
+    pub fn new(connection: MavlinkConnection) -> Self {
+        Self { connection }
+    }
+
+    pub fn handle(&self) -> MavlinkHandle {
+        MavlinkHandle::new(self.connection.clone())
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct MavlinkHandle {
+    #[allow(dead_code)]
+    connection: MavlinkConnection,
+}
+
+impl MavlinkHandle {
+    pub(crate) fn new(connection: MavlinkConnection) -> Self {
+        Self { connection }
+    }
+
+    pub async fn send_raw(&self, _payload: Vec<u8>) -> Result<()> {
+        Err(AutopilotError::NotImplemented(
+            "mavlink_layer::send_raw (AZ-641)",
+        ))
+    }
+
+    pub fn health(&self) -> ComponentHealth {
+        ComponentHealth::disabled(NAME)
+    }
+}
+
+#[async_trait]
+impl MavlinkSink for MavlinkHandle {
+    async fn send_raw(&self, msg: Vec<u8>) -> Result<()> {
+        MavlinkHandle::send_raw(self, msg).await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_compiles() {
+        // Arrange / Act
+        let h = MavlinkLayer::new(MavlinkConnection {
+            uri: "udp://127.0.0.1:14550".into(),
+        })
+        .handle();
+
+        // Assert
+        assert_eq!(h.health().level, shared::health::HealthLevel::Disabled);
+    }
+}