V-L2-O1: init_manifest reads from Default + adds --force / --name flags

[hyperpolymath]

Context

init_manifest writes a hardcoded TOML template that does not
reflect OctadConfig::default(). If defaults change in code, the
template diverges silently.

Also: the init subcommand fails if the file already exists, but
provides no --force to overwrite.

What to do

1. Rebuild the template from OctadConfig::default() rather than
   hardcoding string values.
2. Add init --force (or init --overwrite) to allow regeneration.
3. Add --name flag to set the project name without post-editing.

Acceptance

• Template fields equal Default::default() values
• --force regenerates over existing file
• --name foo sets [project].name = "foo"
• Unit test exercises all three flags