refactor(adapter-riscv): replace hardcoded demo with proper init launch via ELF parsing

Adapter now: parses init binary (ELF or raw), allocates pages, creates
user page table, sets thread entry point in SavedContext, enters U-mode.
Init takes over from there — no more IPC demo hardcoded in the adapter.

crates/adapter-riscv/Cargo.toml

@@ -11,6 +11,7 @@ bench = false
 [dependencies]
 types = { workspace = true }
 domain = { workspace = true }
+elf = { workspace = true }
 platform = { workspace = true }
 kernel = { workspace = true }