Tranche 1 of LST-65 (ProjectManagement module migration). Decouples the
TimeTracking module from the core-business entities before they move, with
no entity relocation yet — keeps the diff minimal and the risk isolated.
- New read contracts in Shared/Domain/Contract (minimal surface, aligned on
the entities' real nullable signatures): ProjectInterface (id/code/name),
TaskInterface (id/number/title), TaskTagInterface (id/label/color),
ClientInterface (id/name).
- Project/Task/TaskTag/Client implement their contract (entities stay in
src/Entity for now). Project.client typed as ClientInterface.
- TimeEntry (TimeTracking) now references ProjectInterface/TaskInterface/
TaskTagInterface instead of the concrete entities; repository + DQL
untouched in behaviour.
- resolve_target_entities maps the 4 contracts to the legacy entities (will
be repointed to the module in tranche 2).
- Adds the migration plan doc.
159 tests green, mapping valid, cs-fixer clean.
Matthieu