cli/serviceability: add ServiceabilityCommand enum with async dispatcher

[juan-malbeclabs]

RFC-20 implementation stack

This PR is part of a 9-PR chain delivering RFC-20: CLI standardization. Each PR's diff is only its own contribution; reviewers should consume them in order.

#	PR	Scope
1	#3753	doublezero-cli-core foundation crate + solana_l1_rpc_url
2	#3754	--solana-url + --log-verbose global flags + tracing init
3	#3755	CliContext built in main + centralized error rendering
4	#3756	rename doublezero_cli → doublezero-serviceability-cli
5	#3757	rewrite location get as the async + CliContext reference verb
6	#3758	docs/cli-standard.md + CLAUDE.md pointer
7	#3779	move per-resource subcommand wrappers into the module crate
8	#3760	add ServiceabilityCommand enum + async dispatcher
9	#3761	#[command(flatten)] + collapse binary dispatch

This PR: #3760 — position 8 of 9. Previous: #3779 · Next: #3761

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Summary of Changes

• Adds doublezero_serviceability_cli::cli::ServiceabilityCommand, the module crate's top-level subcommand enum per RFC-20 §Module contract item 2.
• Aggregates 17 serviceability variants: Init, Migrate, Address, Balance, Config, GlobalConfig, Location, Exchange, Contributor, Permission, Tenant, Device, Link, AccessPass, User, Export, Keygen, Resource.
• Implements async fn execute(ctx: &CliContext, client: &impl CliCommand, out: &mut impl Write) that owns the full per-resource dispatch tree currently inlined in client/doublezero/src/main.rs. The Location::Get arm forwards &ctx and is .awaited (matches the RFC-20 reference verb from cli/serviceability: rewrite location get to rfc-20 conforming pattern #3757); all other resource arms are sync.
• Not yet wired into the unified binary. The next PR (actions: add missing go.{mod,sum} path #9) adds #[command(flatten)] Serviceability(ServiceabilityCommand) to the binary's Command enum and collapses main.rs's ~270-line match block to a single dispatch arm.

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	1	+242 / -0	+242
Scaffolding	1	+1 / -0	+1
Docs	1	+1 / -0	+1
Total	3	+244 / -1	+243

Single new file in the library plus a one-line pub mod in cli/mod.rs. The enum is pub and reachable but currently has no in-tree consumer; it surfaces as the module crate's public mounting point ready for the binary to flatten.

Key files (click to expand)

• smartcontract/cli/src/cli/command.rs (new) - the ServiceabilityCommand enum + async fn execute dispatcher. Forwards &CliContext only to verbs that consume it (today only LocationCommands::Get per cli/serviceability: rewrite location get to rfc-20 conforming pattern #3757); other arms ignore ctx. The AccessPassCommands::Fund arm preserves the existing stdin-reading behavior (std::io::stdin().lock()) since that interaction is part of the verb's contract today.
• smartcontract/cli/src/cli/mod.rs - adds pub mod command;.

Testing Verification

• cargo check --workspace clean.
• make rust-test green workspace-wide (no behavior change — the new enum is unused by the binary in this PR).
• make rust-lint clean.
• cargo doc --no-deps -p doublezero-serviceability-cli succeeds and the new module appears.
• Targets jo/7-cli-serviceability-move-cli-files; the diff shown is only this PR's contribution. Final PR actions: add missing go.{mod,sum} path #9 will flatten this enum into the binary and collapse main.rs dispatch.