monopam: split into one module per command
Reorganize monopam.ml into focused command modules:
- ctx.ml - operational context (fs, package discovery, checkouts)
- init.ml - monorepo initialization and file generation
- pull.ml - pull operations (fetch checkouts, merge subtrees)
- push.ml - push operations (subtree split, export)
- add.ml - add packages to monorepo
- remove.ml - remove packages from monorepo
- clean.ml - clean empty commits from history
- diff.ml - verse collaboration diff operations
Monopam.ml now re-exports modules with backward-compatible
function exports for existing bin commands.