fix(pt): prepend CLUSTER_NAME for restart/reinit/switchover/failover (fixes #29)

[CrzMarvin]

Summary

Fixes #29 — pig pt restart, pig pt reinit, pig pt switchover, and pig pt failover all fail because the underlying patronictl invocation omits the required CLUSTER_NAME positional argument.

Unlike patronictl pause/resume/list, those four subcommands do not accept -c <config> as a substitute for scope — they require CLUSTER_NAME as the first positional argument.

Reproduction (from #29)

$ sudo -u dba pig pt restart --pending -f
$ /usr/bin/patronictl -c /etc/patroni/patroni.yml restart --force --pending
Error: Missing argument 'CLUSTER_NAME'.

$ sudo -u dba pig pt restart pg-nms-1 -f
# patronictl gets `restart --force pg-nms-1` → treats pg-nms-1 as CLUSTER_NAME
# → etcd PermissionDenied (no such cluster key)

$ sudo -u dba pig pt restart pg-nms pg-nms-1 -f
# pig only consumes args[0] = "pg-nms" → patronictl runs `restart pg-nms --force`
# → restarts WHOLE cluster instead of just pg-nms-1 (surprising and undocumented)

Fix shape

• New exported GetClusterName(dbsu) in cli/patroni/patroni.go — reads scope: from /etc/patroni/patroni.yml, falls back to utils.DBSUCommandOutput(dbsu, [\"cat\", DefaultConfigPath]) for the typical Pigsty layout where the file is postgres:postgres 0640.
• Pure args builders extracted: buildRestartArgs / buildReinitArgs / buildSwitchoverArgs / buildFailoverArgs — testable without exec'ing patronictl. Each prepends `cluster` immediately after the verb.
• Restart / Reinit / Switchover / Failover now resolve the cluster name once at the top, then call their respective builder + runPatronictl.
• Misleading comment in original `Restart` ("Since we use -c config, cluster name is auto-detected" — only true for pause/resume/list) removed.

`cli/context/context.go` has a similar helper (`getPatroniClusterName`) — left untouched to keep this PR focused; happy to follow up with a refactor to reuse `GetClusterName` if you'd like.

Tests

`cli/patroni/patroni_test.go` extended:

• `TestBuildRestartArgs` — table-driven, 4 cases (nil opts / pending+force / specific member+force / role filter). Verifies cluster appears at `args[1]` and the flag/positional layout matches patronictl's CLI contract.
• `TestBuildReinitArgs / TestBuildSwitchoverArgs / TestBuildFailoverArgs` — same shape for the other three commands.
• `TestPatronictlPositionalContract` — regression guard. Documents the invariant inline so a future refactor that drops the prepend fails fast with a self-explanatory message.

Validation

• `go build ./...` clean
• `go vet ./...` clean
• `go test ./...` — every package green (`cli/patroni` 3.818s, full suite ~80s)
• Manually exercised the fix path on a 2-node Pigsty v4.3 cluster (Ubuntu 24.04, patroni 4.1.2, etcd3 DCS) — `Restart` now passes through to `patronictl restart pg-nms [member] --force --pending` correctly, clears pending restart markers as expected.

Out of scope (kept minimal)

• `cli/context/context.go`'s `getPatroniClusterName` (duplicate logic) — happy to refactor in a follow-up.
• `buildSwitchoverCommand` / `buildFailoverCommand` (for the Plan display surface) — those return what the user would TYPE (`pig pt switchover ...`), not patronictl args, so they're correct as-is.