feat(skywire-cli): svc gains --testenv + URL overrides + fetch-chain flags; --jq/--shape parity

[0pcom]

Converges the svc command group toward the deployment-selection and structured-output vocabulary the rest of the CLI already uses. Strictly backward-compatible (defaults are prod / empty).

D — deployment-service URL + fetch-flag unification (svc slice)

svc hardcoded deployment.Prod.* in every subcommand and exposed only --direct/--rpc — unlike sd/ut, which offer --testenv and per-service URL overrides, and unlike the fetch-chain flags (--no-cxo/--no-rpc/--no-dmsg) present on ut.

• New persistent flags on svc RootCmd, inherited by every subcommand: --testenv (or SKYWIRETEST=1), --tpdurl/--dmsgdurl/--arurl, and the --no-cxo/--no-rpc/--no-dmsg/--sk/--config fetch-chain controls.
• fetchViaVisorOrDirect resolves each subcommand's base URL via baseURLFor(service) (honors --testenv + overrides) instead of literal deployment.Prod.*.
• svc health's direct queries use the same resolution.

E — structured-output parity

--jq/--shape were accepted but ignored on the svc pretty-print subs (output went through internal.PrintOutput; only ar check used the flag-aware cliout printer). emitPretty now routes --json/--jq/--shape through cliout.Print; the default human view stays pretty-indented JSON.

Validation (standalone + combined binaries built locally)

• go build ./cmd/skywire-cli/ . clean.
• New flags inherited by all svc subs (e.g. svc tpd stats --help, svc health --help show them as Global Flags under the combined binary).
• svc tpd stats --json (compact when piped), --jq 'keys', --jq '.total_transports', --shape all work; bare command still prints pretty JSON.
• svc tpd stats --direct --tpdurl http://127.0.0.1:9 reaches the override URL in the fetch (fails to map, as expected) — proving the override is threaded.

Deferred (design note)

• --rpc/--direct are still registered per-subcommand rather than once on the svc root; left as-is to keep the diff focused and avoid duplicate-flag churn. Folding them onto the root persistent set is a safe follow-up.
• The broader cross-group vocabulary convergence (e.g. sd's --sdurl/--uturl, ut's --url, hidden aliases so every group shares one spelling) is not attempted here — this PR brings svc up to parity as the highest-value slice.
• DmsgURLForHTTP/cxoFeedForURL map only deployment.Prod.* prefixes, so a raw non-prod --*url override (or --testenv) is only fully effective on the --direct path when the target is already a dmsg:// URL. This is a pre-existing fetch-chain property shared with sd/ut, not introduced here; teaching the mapping about deployment.Test.* would be a separate change across the whole CLI.