chore: initial scaffold — workspace, docs, blueprint

Sets up the PiCloud monorepo as a Cargo workspace organised around the
three-service architecture (manager / orchestrator / executor), each
backed by a *-core library crate so the same logic powers both the MVP
all-in-one `picloud` binary and the future split-process cluster mode.

  * crates/shared, executor-core, orchestrator-core, manager-core
    define the library surface and trait seams between the three
    services (`ExecutorClient`, `ScriptResolver`, `ScriptRepository`).
  * crates/picloud is the MVP entrypoint; serves /healthz on 8080
    (override via PICLOUD_BIND).
  * crates/picloud-{manager,orchestrator,executor} are skeleton
    binaries that keep the crate boundaries honest until cluster
    mode is built out in v1.3+.
  * docs/git-workflow.md defines the trunk-based workflow:
    short-lived branches, Conventional Commits, separate hotfix
    flow with mandatory reproduction tests.
  * CLAUDE.md captures the working rules for future Claude sessions.

Workspace passes `cargo fmt`, `cargo clippy -D warnings` (with
pedantic enabled), and `cargo test --workspace`. The all-in-one
binary responds on `/healthz` and `/`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/orchestrator-core/src/client.rs

@@ -0,0 +1,61 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use picloud_executor_core::{Engine, ExecError, ExecRequest, ExecResponse};
+
+/// The seam between the orchestrator and the executor.
+///
+/// Single-node mode plugs in `LocalExecutorClient`, which calls
+/// `executor-core` in-process. Cluster mode plugs in `RemoteExecutorClient`,
+/// which forwards over HTTP to an executor node. Everything else in
+/// orchestrator-core depends only on this trait.
+#[async_trait]
+pub trait ExecutorClient: Send + Sync {
+    async fn execute(&self, source: &str, req: ExecRequest) -> Result<ExecResponse, ExecError>;
+}
+
+/// In-process executor — wraps `executor-core::Engine` directly.
+pub struct LocalExecutorClient {
+    engine: Arc<Engine>,
+}
+
+impl LocalExecutorClient {
+    #[must_use]
+    pub fn new(engine: Arc<Engine>) -> Self {
+        Self { engine }
+    }
+}
+
+#[async_trait]
+impl ExecutorClient for LocalExecutorClient {
+    async fn execute(&self, source: &str, req: ExecRequest) -> Result<ExecResponse, ExecError> {
+        self.engine.execute(source, req).await
+    }
+}
+
+/// Remote executor — forwards to a peer executor node over HTTP.
+///
+/// Skeleton only; fleshed out when cluster mode lands.
+pub struct RemoteExecutorClient {
+    _client: reqwest::Client,
+    _base_url: String,
+}
+
+impl RemoteExecutorClient {
+    #[must_use]
+    pub fn new(base_url: impl Into<String>) -> Self {
+        Self {
+            _client: reqwest::Client::new(),
+            _base_url: base_url.into(),
+        }
+    }
+}
+
+#[async_trait]
+impl ExecutorClient for RemoteExecutorClient {
+    async fn execute(&self, _source: &str, _req: ExecRequest) -> Result<ExecResponse, ExecError> {
+        Err(ExecError::Runtime(
+            "RemoteExecutorClient not implemented (cluster mode is v1.3+)".into(),
+        ))
+    }
+}