wire generated CLI commands into main.rs

[MintsInc]

Context

PR #651 (#651) is openapi-transformer's first end-to-end run generating pup CLI command modules from the OpenAPI spec (src/generated.rs, src/downtime.rs). Nothing in main.rs referenced either file, so they were dead code — not compiled, not linted, not reachable by any command. This PR wires them in.

Note: this branch was cut from #651's branch, so it carries #651's commit plus the wiring change. Intent is for this PR to merge first (landing both the generated files and the wiring together); #651 should then be closed or rebased as a no-op.

Changes

Added mod generated alongside the other top-level module declarations, and flattened GeneratedCommand into the Commands enum with #[command(flatten)] rather than nesting it under a pup generated subcommand — this keeps the generated surface as top-level peers (pup downtime get ..., not pup generated downtime get ...), matching how every other domain is exposed today. generated.rs is designed as the stable, one-time integration point: future openapi-transformer regenerations only add variants inside that file and never need to touch main.rs again.

Known blocker, not resolved here: pup already hand-writes a top-level downtime command (list/get/create/cancel). The generated GeneratedCommand::Downtime collides with it on the subcommand name — clap's debug assertion panics at runtime ("command name downtime is duplicated") on any invocation that builds the full Command tree (e.g. pup --no-agent --help). This is a product decision — retire/merge the hand-written downtime command, or pick a different pilot operation upstream in datadog-api-spec — not something resolved unilaterally in this PR.

Tests

• cargo build and cargo clippy --all-targets -- -D warnings pass.
• cargo test passes, including the generated tier-1 smoke test in downtime.rs (it exercises downtime::get directly, not through clap parsing, so it doesn't hit the collision).
• cargo fmt --check fails, but only inside the generated src/downtime.rs file itself (two multi-line #[arg(long)] formatting diffs) — not touched here since it's marked "DO NOT EDIT" and is upstream's generated output.
• Manually confirmed the collision: pup --no-agent --help panics with "Command pup: command name downtime is duplicated". This PR should not merge until that's resolved.

[MintsInc]

Superseded — reworked to avoid pulling in #651's commit. See replacement PR.