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/executor-core/src/lib.rs

@@ -0,0 +1,17 @@
+//! Rhai script execution: engine, sandbox, SDK bindings.
+//!
+//! This crate has no Postgres dependency and no awareness of HTTP. It is
+//! used both by the orchestrator (in-process, via `LocalExecutorClient`) and
+//! by the standalone executor binary (in cluster mode). Keep it that way.
+
+pub mod context;
+pub mod engine;
+pub mod logging;
+pub mod sandbox;
+pub mod types;
+
+pub use engine::Engine;
+pub use sandbox::Limits;
+pub use types::{
+    ExecError, ExecRequest, ExecResponse, ExecStats, InvocationType, LogEntry, LogLevel,
+};