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/sandbox.rs

@@ -0,0 +1,37 @@
+/// Resource and capability limits applied to every script execution.
+///
+/// Defaults are conservative and safe to expose to untrusted Rhai sources.
+/// Per-script overrides (e.g. higher operation budgets) come from the
+/// `Script` config and are clamped against these as upper bounds.
+#[derive(Debug, Clone, Copy)]
+pub struct Limits {
+    /// Hard cap on Rhai operations executed per invocation.
+    /// Doubles as a CPU-time proxy without needing real timers.
+    pub max_operations: u64,
+
+    /// Max length of any single string the script constructs.
+    pub max_string_size: usize,
+
+    /// Max number of elements in any array.
+    pub max_array_size: usize,
+
+    /// Max number of properties in any object/map.
+    pub max_map_size: usize,
+
+    /// Max call/expression nesting depth.
+    pub max_call_levels: usize,
+    pub max_expr_depth: usize,
+}
+
+impl Default for Limits {
+    fn default() -> Self {
+        Self {
+            max_operations: 1_000_000,
+            max_string_size: 64 * 1024,
+            max_array_size: 10_000,
+            max_map_size: 10_000,
+            max_call_levels: 64,
+            max_expr_depth: 64,
+        }
+    }
+}