truapi-host: derive the product id from the product manifest

Part of #517.

Context

localhost:3000 is the wrong default for most real work. A product usually wants the dotNS identity it ships under, peopl.<tld> for the network being targeted, so that accounts, storage and permissions match the deployed product rather than a local origin.

The manifest already carries that identity: LocalProductConfig.productName is the product's dotNS base name (see docs/rfcs/product-manifest.md). The CLI should read it instead of making the developer repeat it on the command line.

Required behavior

• The CLI reads the product's local manifest config from the working directory and uses productName as the product id.
• The top-level domain follows the selected --network, so one manifest serves .dot, .paseo and .test runs.
• --product-id still overrides the manifest.
• The local-origin default applies only when no manifest is found.
• Startup output names the product id and where it came from: manifest, flag, or origin default.

Related: #515, which asks for the same thing from the host side ("i can open localhost:3000 from any host and it is peopl.dot for truapi").

Start with the CLI entry point and read docs/rfcs/product-manifest.md for LocalProductConfig.productName and manifest behavior. Trace how --network and --product-id are handled, then verify that the manifest, flag, and origin-default sources are reported correctly in startup output and that the local-origin fallback remains available.