chore(make): add a debugger target that builds the host in dev mode

[decrypto21]

Adds a make debugger target that starts the wire debugger against a host that can reach it, with nothing to enable by hand.

Why: make dev cannot drive the debugger. dotli ships only build and preview, both production builds, and the dial sits behind import.meta.env.DEV, which a production bundle replaces with false. The host never dials, the board stays empty, and nothing reports why.

How: Makefile builds the dotli host in dev mode and runs the debugger, the host preview and the playground together. create-worker-host-runtime.ts lets that build's dial URL reach the host, so the dial URL now has two sources: a localStorage key as before, and a value the dev build carries in VITE_TRUAPI_DEBUGGER. Both sit inside the same DEV gate, so a production bundle still resolves neither.

• A key set by hand wins, so the build's value is a default rather than an override, and the host reports which source it used.
• DEBUGGER_PORT moves the server port and the baked-in URL together. Moving one alone leaves the host dialling a dead port, which presents as a broken debugger.
• The debugger runs from the workspace, so nothing here waits on @parity/truapi-debugger being published.

Verified with no key set. Against dot.li main, which carries no seeding of its own, a fresh browser profile with empty localStorage reports wire debugger: dialling ws://127.0.0.1:9231 from the build. 92 @parity/truapi-host tests pass. The printed block, truapi-host's README and §9 of the design doc are updated to describe both sources.

Not exercised from a pristine clone: dev-bootstrap runs git submodule update, which aborts while the dotli submodule carries local work.