fix(database): make database link usable (crash + port type + payload key)

[heathweaver]

What

deno deploy database link is currently unusable. This makes it work end to end. It turned out to be three distinct bugs, each blocking the one after it.

Fixes #104.

Bug 1 — unconditional crash

--hostname/--username/--password/--port are declared conflicts: ["connectionString"], but connectionString is a positional argument, not an option. Cliffy's conflicts only accepts option names, so validation throws Unknown conflicting option "connectionString" before any input is processed — every form crashes, including database link --help.

Fix: remove the invalid conflicts (and the required: true on --hostname, which otherwise makes the connection-string form impossible), and validate the connection-string-vs-flags mutual exclusion manually in the action.

Bug 2 — port sent as a string

With the crash fixed, the backend rejects the request: port: expected number, received string. Both --port <number> (cliffy treats <number> as a value label, not a type coercion) and the parsed connection-string port arrive as strings. Fix: coerce port to a number when building connectionConfig.

Bug 3 — wrong payload key for createInstance

With ports fixed, --dry-run succeeds but a real link still fails with connection_config: expected object, received undefined. The dry-run path sends connection_config (snake_case) to databases.testConnection, but the link path sent connectionConfig (camelCase) to databases.createInstance. The backend expects snake_case. Fix: use connection_config in the createInstance call too.

Verification

Against a real Postgres, all paths now work:

$ deno run -A main.ts database link --dry-run my-db --hostname db.example.com --port 5432 --username u --password '***'
✔ Connection test successful.

$ deno run -A main.ts database link --dry-run my-db "postgresql://u:***@db.example.com:5432/db"
✔ Connection test successful.

$ deno run -A main.ts database link my-db "postgresql://u:***@db.example.com:5432/db"
✔ Successfully linked database 'my-db'.

deno fmt and deno lint pass on the changed file.