feat: model repo standards and detect prefix collisions

Implement RMGR-WP-0004 T01 (flavor, required files, anti-patterns from
canon) and T08 (prefix ownership registry plus uniqueness scan).
rmgr conform and rmgr prefix-uniqueness are detection only.

docs/repository-standards_v0.1.md

@@ -0,0 +1,35 @@
+# Repository standards v0.1
+
+Repo Manager **implements** Custodian canon. It does not author a second
+definition. This note is an index.
+
+| Concern | Canon |
+| --- | --- |
+| Categories and `.repo-classification.yaml` | `the-custodian/canon/standards/repo-classification-standard_v1.0.md` |
+| `prj-` layout, `GOAL.md`, anti-pattern both purpose docs | `the-custodian/canon/standards/project-repository-flavor_v0.1.md` |
+| One workplan prefix per repository | `the-custodian/canon/architecture/adr-007-workplan-identity-and-repo-worker-topology.md` |
+
+## Flavor resolution
+
+Precedence, then warn on disagreement (do not silently pick a winner for
+operators — the first match is used only to choose the required-file set):
+
+1. `.repo-classification.yaml` `category`
+2. `GOAL.md` `repo_flavor`
+3. slug prefix `prj-`
+
+`prj-` layout (`GOAL.md`, no `INTENT.md`) applies when the slug starts
+with `prj-` or `GOAL.md` declares `repo_flavor: project`. Not every
+`category: project` repo is a `prj-` repo.
+
+## Commands
+
+```bash
+rmgr conform --path .
+rmgr prefix-uniqueness --root ..
+```
+
+`prefix-uniqueness` is detection only. It does not rename files.
+Registry: [`config/workplan-prefix-registry.yaml`](../config/workplan-prefix-registry.yaml).
+
+Work: `RMGR-WP-0004-T01`, `RMGR-WP-0004-T08`.