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/shared/src/ids.rs

@@ -0,0 +1,52 @@
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+macro_rules! id_type {
+    ($name:ident) => {
+        #[derive(
+            Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize,
+        )]
+        #[serde(transparent)]
+        pub struct $name(pub Uuid);
+
+        impl $name {
+            #[must_use]
+            pub fn new() -> Self {
+                Self(Uuid::new_v4())
+            }
+
+            #[must_use]
+            pub fn into_inner(self) -> Uuid {
+                self.0
+            }
+        }
+
+        impl Default for $name {
+            fn default() -> Self {
+                Self::new()
+            }
+        }
+
+        impl From<Uuid> for $name {
+            fn from(u: Uuid) -> Self {
+                Self(u)
+            }
+        }
+
+        impl From<$name> for Uuid {
+            fn from(id: $name) -> Self {
+                id.0
+            }
+        }
+
+        impl std::fmt::Display for $name {
+            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                self.0.fmt(f)
+            }
+        }
+    };
+}
+
+id_type!(ScriptId);
+id_type!(ExecutionId);
+id_type!(RequestId);