fix: resolve audit findings — stale text, dead code, build tags, docs

Assisted-by: MiMo V2.5 Pro

docs/CLI.md

@@ -52,7 +52,7 @@ Rules: `unknown-instruction`, `operand-count`, `undefined-label`,
 
 ## `gasm asm [--format raw|elf|goobj] [-p pkg] [-o out] <file>`
 
-Assemble FILE (amd64) to machine code.
+Assemble FILE to machine code (amd64, arm64, riscv64, loong64).
 
 | Flag | Description |
 |------|-------------|
@@ -90,7 +90,7 @@ return values and any output written to the buffers.
 
 ## `gasm debug --func <name> [--buf spec] <file.s>`
 
-Interactive debugger for JIT-assembled amd64 functions. Requires a
+Interactive debugger for JIT-assembled functions (amd64, arm64, riscv64, loong64). Requires a
 compiled binary on `$PATH` (not `go run`).
 
 | Flag | Description |