Document Packit RPM distribution pipeline in ARCHITECTURE.md

The release pipeline diagram only covered the PyPI flow, but the
same release event also fires Packit to build and ship Fedora and
EPEL RPMs in parallel. Add the missing components (.packit.yaml,
python-bitmath.spec, Packit, Copr, dist-git, Koji, Bodhi) to the
component inventory and a second diagram showing the RPM
distribution path alongside the existing PyPI path.

Notes the known-stale target matrix (fedora-rawhide, fedora-42,
epel-9, epel-10) so the document does not pretend to be current
on that front.

Author: timlnx

ARCHITECTURE.md

@@ -169,6 +169,13 @@ model.
 | PyPI Trusted Publishing | PyPI's OIDC verifier | Validates the OIDC token from the `publish.yml` workflow and authorizes the upload |
 | PyPI | pypi.org | The distribution channel; serves wheels and sdists over HTTPS to `pip` |
 | Read The Docs | bitmath.readthedocs.io | Hosts the rendered documentation; rebuilds on push to master |
+| `.packit.yaml` | Repository root | Packit configuration; declares which release events trigger Copr scratch builds, dist-git PRs, Koji builds, and Bodhi updates |
+| `python-bitmath.spec` | Repository root | RPM packaging spec used by Packit to build Fedora and EPEL RPMs |
+| Packit | packit.dev | Hosted automation that connects upstream releases to Fedora dist-git, Copr, Koji, and Bodhi based on `.packit.yaml` |
+| Copr | copr.fedorainfracloud.org/coprs/tbielawa/bitmath-ci | Fedora's build-on-demand farm; used for PR scratch builds and release-candidate builds |
+| Fedora dist-git | src.fedoraproject.org/rpms/python-bitmath | Where the official RPM source lives for each Fedora/EPEL branch |
+| Koji | koji.fedoraproject.org | Fedora's official build system; produces the RPMs that ship to users |
+| Bodhi | bodhi.fedoraproject.org | Fedora's update system; pushes Koji-built RPMs to stable for f42, epel9, and epel10 |
 
 ### Pipeline View
 
@@ -218,6 +225,80 @@ model.
                   +------------------------+
 ```
 
+### RPM Distribution Path (Fedora and EPEL via Packit)
+
+The same `release: published` event that triggers `publish.yml` also
+fires the Packit pipeline. The two paths run in parallel and are
+independent of each other; PyPI consumers get the wheel, Fedora and
+EPEL consumers get an RPM. Production releases (clean `vX.Y.Z` tags)
+flow through `propose_downstream` to dist-git, Koji, and Bodhi.
+Release-candidate tags (`vX.Y.Z-rcN`) take a shorter path that only
+produces Copr builds for testing.
+
+```
+                  +------------------------+
+                  | release: published     |
+                  | (same event that fires |
+                  | the publish.yml flow   |
+                  | above)                 |
+                  +-----------+------------+
+                              | reads .packit.yaml
+                              v                + python-bitmath.spec
+                  +------------------------+
+                  | Packit                 |
+                  |                        |
+                  | clean vX.Y.Z tag:      |
+                  |   propose_downstream   |
+                  |   opens dist-git PRs   |
+                  |   for rawhide, f42,    |
+                  |   epel9, epel10        |
+                  |                        |
+                  | vX.Y.Z-rcN tag:        |
+                  |   copr_build only      |
+                  +-----------+------------+
+                              | dist-git PR merged
+                              v
+                  +------------------------+
+                  | Fedora dist-git        |
+                  |   src.fedoraproject    |
+                  |   .org/rpms/           |
+                  |   python-bitmath       |
+                  +-----------+------------+
+                              | commit trigger
+                              v
+                  +------------------------+
+                  | Koji                   |
+                  |   builds RPMs from     |
+                  |   each dist-git branch |
+                  +-----------+------------+
+                              | tagged build
+                              v
+                  +------------------------+
+                  | Bodhi                  |
+                  |   update_type:         |
+                  |   enhancement;         |
+                  |   stable push for      |
+                  |   f42, epel9, epel10   |
+                  |   (rawhide skipped)    |
+                  +-----------+------------+
+                              | dnf install python-bitmath
+                              v
+                  +------------------------+
+                  | Fedora / EPEL consumer |
+                  +------------------------+
+```
+
+The Copr scratch-build job that fires on every pull request is not
+shown above; it is a CI-style validation, not part of the release
+pipeline. It uses the same `.packit.yaml` and spec file to confirm
+the RPM still builds across the targeted Fedora and EPEL branches
+before a change merges.
+
+**Known limitation**: the target matrix in `.packit.yaml` today is
+`fedora-rawhide`, `fedora-42`, `epel-9`, and `epel-10`. As new
+Fedora and EPEL releases land, that list needs to be refreshed. That
+work is tracked outside this document.
+
 ### Actions
 
 1. **Version bump.** I edit `VERSION` to the new SemVer string.