cli: add --solana-url and --verbose global flags

[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	#3759	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: #3754 — position 2 of 9. Previous: #3753 · Next: #3755

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Summary of Changes

• Adds the --solana-url <SOLANA_RPC_URL> global flag to doublezero per RFC-20 §Global flags. Distinct from --url, which continues to override the DZ ledger transport; --solana-url targets the Solana L1 transport. The flag is parsed and exposed on the binary's App struct; per-verb consumption lands when verbs migrate to construct typed Solana L1 clients from CliContext (follow-up PRs).
• Adds the --verbose / -v (repeatable) global flag and initializes the tracing subscriber at startup via doublezero_cli_core::init_logging(verbosity). Default level is warn; -v raises to debug, -vv to trace. Honors the RUST_LOG env var when set. Diagnostic logs go to stderr so --json output on stdout remains parseable.
• Replaces the println!("using keypair: ...") startup line with a tracing::info! event so the keypair confirmation now appears only at -v or higher and no longer pollutes parseable stdout.

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	1	+13 / -1	+12
Config/build	2	+3 / -0	+3
Docs	1	+2 / -0	+2
Total	4	+18 / -1	+17

Three new global flags wired into the binary and the logging facade; no changes to subcommand dispatch or verb behavior.

Key files (click to expand)

• client/doublezero/src/main.rs - adds solana_url and verbose fields to the App struct, calls doublezero_cli_core::init_logging(app.verbose) first thing in main, and replaces the println! keypair confirmation with tracing::info!.
• client/doublezero/Cargo.toml - depends on doublezero-cli-core and tracing.

Testing Verification

• make rust-lint clean.
• doublezero --help shows the new --solana-url and --verbose / -v global flags with the expected help text.
• doublezero --keypair /tmp/fake.json --env local -v address emits a tracing::info! event with the keypair path on stderr while stdout shows only the address; no -v keeps stderr empty.
• Built on top of cli/core: introduce doublezero-cli-core crate and solana_l1_rpc_url #3753 (foundation crate); this PR targets jo/1-cli-core-foundation and the diff shown is its own contribution only.