fix: validate init template flags before the non-empty-directory prompt

[Bccorb]

Problem

seamless init --bogus in a non-empty directory asks the destructive overwrite question
before it ever discovers the flag is unknown.

The order in src/commands/init.ts is:

1. scaffold() reads the directory and, when it is not empty, calls
   chooseExistingDirectoryAction() (src/prompts/initMode.ts),
   which prompts "Scaffold a project here anyway? Starter files overwrite anything with the
   same name."
2. Only after that does scaffoldLocal() / scaffoldManaged() call
   resolveTemplateAliases(), which is what throws Unknown option "--bogus".

So a typo, or the documented "run an unknown flag to see the available examples" hint, both
route a developer through an overwrite prompt on the way to an error. The default is No and
it requires explicit confirmation, which is what keeps this from being a data-loss bug, but
the common scripted pattern of piping y at the first prompt turns it into one.

PR #148 fixed the worst instance of this (--help / -h are now handled ahead of every
command's own parsing), but any other unrecognized flag still takes the same path.

Change

• Resolve and validate template flags in runCLI() before scaffold() touches the
  filesystem, so an unknown or conflicting flag exits non-zero with the available flags
  listed and nothing is prompted.
• Keep the existing error text from resolveTemplateAliases(); only the timing moves.
• Drop the "Run an unknown flag to see the available examples" line from the init help body
  in src/commands/helpTopics.ts. Discovery belongs in
  seamless templates list (separate issue), not in an error path.

Acceptance

• seamless init --bogus in a directory full of files errors immediately, prompts nothing,
  and exits non-zero.
• Conflicting flags (two web templates) behave the same way.
• A valid flag still reaches the existing-directory prompt exactly as it does today.
• Unit test covering "unknown flag in a non-empty directory never calls the prompt".