Parse CLI arguments with effect/unstable/cli

[FreshlyBrewedCode]

Parent

#32

What to build

factory parses its own arguments with effect/unstable/cli instead of four hand-rolled parsers.
Every existing command keeps its current surface — init, serve, start, runs, log, run,
with the same flags, the same defaults, the same exit codes and the same $FACTORY_URL fallback —
but help text is generated rather than hand-maintained, flag values are validated before they reach
a command body, and the argv layer becomes testable.

Today's parsers disagree with each other in ways that are defects, not style: parseFlags walks
argv at stride 2 and so structurally cannot represent a boolean flag (one --watch and every
subsequent pair is misread), which is why factory start needed a second, different parser;
init's flags are parsed inline in the import.meta.main block; and serve passes an unvalidated
Number(portRaw) straight to Bun.serve, so --port abc becomes NaN. Because usageError
calls process.exit inside a parser, none of this can be tested, and every current CLI test
bypasses argv and calls the command functions with structured options.

The command bodies themselves stay as they are — plain async functions — wrapped at the boundary.
This ticket does not change what any command does.

See ADR 0009 §5 (docs/adr/0009-imperative-workflows-effect-boundary.md) for why the CLI is the
one place the boundary moves first.

Acceptance criteria

• Every command and flag documented in the current USAGE string works identically, including --watch, $FACTORY_URL, and the --clone/--git-name/--git-email group
• --port and any other numeric flag reject a non-numeric value with a clear error instead of passing NaN downstream
• Help output is generated by the CLI definition; the hand-maintained USAGE constant is gone
• Exit codes are unchanged: 0 completed, 1 failed, 130 cancelled
• Argv parsing is covered by tests that feed argv directly, rather than bypassing it
• No process.exit call remains inside a parsing function
• bun run check passes

Blocked by

None (can start immediately).