An AI agent skill for Odoo's git conventions

Commit message

[ADD] skills: odoo-git, commit and pull request conventions

Odoo's commit and pull request conventions are spread across the git
guidelines, the contribution wiki, and merge-bot behavior. An agent
writing a commit or choosing a target branch needs one reference.

Add a skill covering the commit header and tags, module and subsystem
scopes, why-first bodies with the steps to reproduce a bug or the
benchmark of a performance change, the references authors write versus
the metadata the bots add, and the branch and pull request rules:
target choice, naming, odoo-dev versus forks, rebase and
force-with-lease.

The skill also says where each part of a message comes from. The diff
gives the what; the ticket, task, or reporter gives the why and the
reported scenario; a benchmark comes from a run. Reading the code tells
what it can do wrong, never what was reported. An agent that lacks a
part asks for it, or writes from the code and the tests, labels those
parts as derived, and offers to amend. Without that rule, an agent
recreating the message of a real fix from its diff presented a scenario
inferred from the code as the reported bug and left no trace of the
difference.

Validation: 5,000 master commit messages from each of Community and
Enterprise compared with the official guidelines, sampled PR metadata,
merge-bot source, and four runs recreating the message of a merged fix
from its uncommitted diff.