Phase 5: Alembic baseline, per-site deploy, ADRs to docs/adr

Migration runner ready and a sister site can deploy from a clean
checkout with one .env file.

ADRs relocated (migrations/adr/ -> docs/adr/):
- migrations/ is now Alembic territory, not docs.
- All cross-references updated: CLAUDE.md, docs/PLUGIN-HOOKS.md,
  docs/PLUGIN-QUICKSTART.md.

Alembic initialized (migrations/):
- env.py, script.py.mako, alembic.ini copied from Flask-Migrate
  templates so `flask db migrate` and `flask db upgrade` work without
  a one-time `flask db init` (which would clash with the existing
  migrations/ directory).
- Baseline migration generated via autogenerate, captures all 47
  tables (core models + 6 plugins) as the upgrade target. Ready for
  per-site `flask db upgrade` from an empty schema.

Deploy artifacts:
- Dockerfile: python:3.12-slim base, gunicorn server, non-root user,
  healthcheck against /api/auth/login. Single image bundles all six
  plugins; sites enable via `flask plugin install <name>`.
- docker-compose.yml: MySQL 8 + API container, healthcheck-gated
  startup, env-driven secrets that fail loud on missing values
  (`${SECRET_KEY:?}` form).
- .env.example: full env-var inventory with comments. Calls out
  required vs optional. Matches what ProductionConfig.validate
  enforces.

docs/DEPLOY.md:
- Step-by-step per-site runbook: clone, configure .env, bring up
  stack, run migrations, seed reference data, install plugins,
  create admin, front with TLS, backups, updates.
- Common-issues table.
- Cross-links to ADR-004 (per-site rationale), ADR-003 (plugin
  distribution), and the config source.

Skills:
- migrating-asset-schema: Alembic + one-shot data migration policy.
  Rules: additive first, renames are three steps, destructive ops
  need rollback, equipment migration filter per ADR-001 + ADR-005.
- hardening-flask-config: production validation, CORS allowlist
  policy, JWT cookie hardening, per-site deploy isolation per ADR-004.

CLAUDE.md updated to reflect the post-Phase-5 state. No tests added
this commit; the Alembic baseline is exercised by the existing
db.create_all-based test suite (tests do not touch the migration
runner; that's by design until per-plugin migrations land).

Test count unchanged: 101 passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/adr/ADR-002-plugin-versioning.md

@@ -0,0 +1,60 @@
+# ADR-002: Plugin contract versioning
+
+- **Status:** ACCEPTED
+- **Date:** 2026-05-08
+- **Deciders:** cproudlock
+- **Supersedes:** none
+
+## Context
+
+Once sister sites start writing their own plugins (or pulling community plugins), the framework's plugin contract becomes a public API. Without a versioning story, any change to `BasePlugin` or the core platform models can silently break installed plugins at remote sites.
+
+The existing `BasePlugin` and `PluginMeta` already declare a `core_version` field (default `">=1.0.0"`), but it is not enforced anywhere. The plugin loader does not check it before instantiation.
+
+## Decision
+
+The framework adopts **semantic versioning for the plugin contract**, declared in two places:
+
+1. **Framework version** (`shopdb/__init__.py`): a single `__contract_version__` constant. This is the version of the platform contract as defined in ADR-001. Bumped according to semver:
+   - **Major**: breaking change to `BasePlugin` ABC, `PluginMeta` schema, or any model in the platform contract (`Asset`, `AssetType`, `AssetStatus`, `AssetRelationship`, `Vendor`, `Location`, `BusinessUnit`, `Model`, `OperatingSystem`).
+   - **Minor**: additive change (new optional hook, new field on a contract model with default).
+   - **Patch**: bug fix, no contract surface change.
+2. **Plugin requirement** (`plugins/<name>/manifest.json`): the existing `core_version` field, expressed as a semver range (e.g., `">=1.0.0,<2.0.0"`).
+
+The plugin loader (`shopdb/plugins/loader.py`) checks `core_version` against `__contract_version__` at load time. Mismatch in dev = re-raise (fail loud). Mismatch in prod = log error, mark plugin as incompatible, exclude from registration.
+
+The `__contract_version__` starts at **`1.0.0`** when ADR-001 is accepted and the `Machine` retirement migration is complete (whichever comes later). Until then, the framework is pre-1.0; plugins should declare `core_version: ">=0.1.0,<1.0.0"`.
+
+## Consequences
+
+### Positive
+
+- Sister sites can pin a known-good framework version. They will not be silently broken when the framework is upgraded.
+- Plugin authors know what counts as a breaking change because the contract surface is enumerated in ADR-001.
+- The loader fails predictably: a mismatched plugin is reported, not silently disabled.
+
+### Negative / cost
+
+- Discipline required: every change to the contract surface must be classified (major / minor / patch). Adding a `version-bump` skill (or a check in code review) reduces the chance of mis-classification.
+- `__contract_version__` becomes a coupling point. Forgetting to bump it after a breaking change means downstream plugins crash silently at runtime instead of failing at install.
+
+### Neutral
+
+- Existing plugins (`plugins/printers/`, etc.) ship as part of the framework, so their `core_version` is always the current `__contract_version__`. The discipline matters mostly for external / sister-site plugins.
+
+## Alternatives considered
+
+1. **No versioning, just trust.** Works for an in-tree-only world. Fails the moment a sister site ships its own plugin. Rejected.
+2. **Calendar versioning** (e.g., `2026.05.0`). Easier to bump, harder to communicate breaking changes. Rejected; semver is the industry standard for library-like contracts.
+3. **Per-hook versioning.** Each hook has its own version. Too granular; plugins still couple to multiple hooks. Rejected.
+
+## Open questions
+
+- When does the framework declare `1.0.0`? Tied to ADR-001 (Asset retirement of Machine) and the framework being deemed "ready for sister sites". Best-effort target: end of Phase 5 in the refactor plan.
+- Should `core_version` accept commercial-grade ranges (`^1.0.0`) or stick to PEP 440 / npm-style ranges? Recommend pip-style (`>=,<`) to match Python ecosystem.
+
+## References
+
+- `shopdb/plugins/base.py` (PluginMeta declaration)
+- `shopdb/plugins/loader.py` (where the version check belongs)
+- ADR-001 (defines what is in the contract)