The version bump example showed `recipe-name: Update to vX.Y.Z`, which
does not follow the practice established in the OpenEmbedded community,
where recipe upgrades record both the old and the new version.

Use `recipe-name: upgrade vX.Y.Z -> vA.B.C` to match that convention.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
(cherry picked from commit c1ec2a5)

Contributors and automation agents lacked a clear, shared specification
for how to contribute and how commits should be structured, which led to
inconsistent subjects and commit messages that merely restated the diff
or bundled unrelated changes together. The guidance also risked being
duplicated and drifting apart between README.md and AGENTS.md.

Add a dedicated CONTRIBUTING.md as the single source of truth for the
contribution workflow and commit conventions. Describe the required
`recipe-name: summary of the changes` subject form, spell out the
expectations for the message body (plain English, problem before
solution, imperative actions), require commits to be atomic, and document
the `Signed-off-by` and `Assisted-by` trailers. Reference the new
document from both README.md and AGENTS.md instead of repeating the rules
in each.

Assisted-by: Claude Code:claude-opus-4-8
(cherry picked from commit f5f6a7f)
[DB: also brought "patching" information back to README.md]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

The wrynose-specific backport workflow — the `git cherry-pick -x` path
from master, the exception for wrynose-only changes, the CI-equivalent
checks, and the `[Backport wrynose]` commit message conventions — lived
inline in AGENTS.md and was partly restated in README.md, so it was easy
for the two to drift apart. This branch is the LTS stable branch, where
backporting is the default path, so this guidance deserves a single home
of its own rather than being buried in the agent guide.

Add BACKPORTING.md as the source of truth for the backport workflow, and
reference it from README.md and AGENTS.md instead of spelling the steps
out inline. Trim the now-duplicated backport section in AGENTS.md down to
a pointer, and adapt the CONTRIBUTING.md introduction to state that
changes should be backported from master following BACKPORTING.md.

Assisted-by: Claude Code:claude-opus-4-8
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>