feat(api): streamline generated app authoring

Move the canonical examples toward generated component-root helpers, typed form decoding, async/state handler registration, and derive-driven app/component registry wiring. Tighten requirements and diagnostics for the server-first, selectorless authoring path.

Verified with cargo run -p slhx-xtask -- test, cargo check --workspace, redgate list, redgate refs, redgate health --strict, and git diff --check.

req: canonical/001

req: canonical/003

req: canonical/004

req: dx/002

req: derive_app/001

req: component/003

req: form/004

req: axum_integration/003

Cargo.lock

@@ -401,7 +401,6 @@ dependencies = [
 name = "hemplate-core"
 version = "0.1.0"
 dependencies = [
- "cc",
  "hemplate-parser",
  "thiserror 2.0.18",
  "tree-sitter",
@@ -1397,6 +1396,7 @@ dependencies = [
 name = "slhx-derive"
 version = "0.1.0"
 dependencies = [
+ "proc-macro2",
  "quote",
  "syn",
 ]