[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/shared/src/observability/mod.rs

@@ -0,0 +1,79 @@
+//! Observability initialisation.
+//!
+//! Per `_docs/02_document/deployment/observability.md`, the autopilot emits
+//! JSON-formatted log records to stdout containing at least: `ts`, `ts_mono_ns`,
+//! `level`, `target`, `event`. Initialisation reads the `RUST_LOG` env var (or
+//! the `default_log_filter` config fallback) and the `log_format` setting.
+
+use tracing_subscriber::{fmt, prelude::*, EnvFilter};
+
+/// Output format for the tracing layer.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum LogFormat {
+    /// Structured JSON to stdout — production default.
+    Json,
+    /// Human-readable colour output — dev shells only.
+    Pretty,
+}
+
+impl LogFormat {
+    pub fn parse(s: &str) -> Self {
+        match s {
+            "json" => LogFormat::Json,
+            "pretty" => LogFormat::Pretty,
+            _ => LogFormat::Json,
+        }
+    }
+}
+
+/// Initialise `tracing-subscriber` with the configured format and filter.
+///
+/// `default_filter` is used when the `RUST_LOG` env var is unset.
+/// Safe to call exactly once at startup.
+pub fn init(
+    format: LogFormat,
+    default_filter: &str,
+) -> Result<(), tracing_subscriber::util::TryInitError> {
+    let env_filter =
+        EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(default_filter));
+
+    let registry = tracing_subscriber::registry().with(env_filter);
+
+    match format {
+        LogFormat::Json => registry
+            .with(
+                fmt::layer()
+                    .json()
+                    .with_target(true)
+                    .with_current_span(false)
+                    .with_span_list(false),
+            )
+            .try_init(),
+        LogFormat::Pretty => registry.with(fmt::layer().with_target(true)).try_init(),
+    }
+}
+
+/// Canonical log field constants (mirrors observability.md §2).
+pub mod fields {
+    pub const TS: &str = "ts";
+    pub const TS_MONO_NS: &str = "ts_mono_ns";
+    pub const LEVEL: &str = "level";
+    pub const TARGET: &str = "target";
+    pub const EVENT: &str = "event";
+    pub const FRAME_SEQ: &str = "frame_seq";
+    pub const POI_ID: &str = "poi_id";
+    pub const COMMAND_ID: &str = "command_id";
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn log_format_parses_known_values() {
+        assert_eq!(LogFormat::parse("json"), LogFormat::Json);
+        assert_eq!(LogFormat::parse("pretty"), LogFormat::Pretty);
+        // Unknown values fall back to JSON (the production-safe default).
+        assert_eq!(LogFormat::parse("xml"), LogFormat::Json);
+    }
+}