feat: enforce input_schema at call time (ADR-016 INVALID_INPUT leg)

- OperationSpec.input_schema was advertise-only: services/schema
  disclosed it but no dispatch entry point consulted it (the only
  enforced schema was publish_schema per-chunk on Pub ops, P-03).
- compile input_schema once at registration, same fail-closed rule as
  publish_schema/CF-003: an un-compilable schema is a registration
  error, never a silently-skipped contract. Validator cache mirrored
  on fork and in OperationRegistryBuilder like the publish validators.
- check after the ACL gate in all three dispatch entry points:
  invoke, invoke_streaming, invoke_sink (via resolve_sink_handler,
  preserving the P-08 single-source-of-truth property). Violations
  return INVALID_INPUT with the input echoed in details.
- raw-JSON-Schema semantics (permissive on unknown keys); adapters
  wanting closed-by-default keep their own hardening (alkhttp's
  CompiledInputSchema composes unchanged).
- motivated by alktty review #001 L1: the channels open-op wrapper
  hands the registry-checked input to the OpenHandler as the
  authoritative params, which requires the registry to validate it.

Verification: cargo test 596 lib (6 new: invoke/streaming/sink
enforcement, fail-closed registration, permissive-{} compile,
fork-carries-validator); --all-features 613; clippy -D warnings
clean; fmt clean; doc 0 warnings; publish --dry-run ok. alkhttp
438+16 tests pass against 0.3.1 (registry) — re-verify against the
published 0.4.0 after upload.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "alkcall"
-version = "0.3.1"
+version = "0.4.0"
 edition = "2021"
 rust-version = "1.85"
 license = "MIT OR Apache-2.0"