feat(jpa): implement the JPA relational persistence platform

Implements the Stable and Experimental JPA persistence platform designs
against real PostgreSQL, adapted to this repository's fail-closed 19-leaf
registry.

The design models the platform as 25 Gradle projects. `src/settings.gradle`
throws unless the registry holds exactly 19 leaves, so the plan's modules
become packages inside `:adapter:outbound:persistence-jpa` (starter in
`:app-bootstrap`, testkit in its own source set). The full mapping, the
renames this repository's naming gate required, and every deliberate
substitution are recorded in `docs/jpa/repository-adaptation.md`.

Seven Docker-backed lanes replace the plan's seven JVM test suites. Each
fails closed: a lane that discovers nothing, or a container that cannot
start, is an error rather than a skip.

Three defects the contracts found against a real server:

- `CommitFailureClassifier` treated only SQLSTATE 40003, class 08, and
  transport breaks as completion-unknown. A backend terminated mid-commit
  reports 57P01, and the commit record may already be in the WAL — so a
  possibly-committed transaction could be re-run. 57P01/57P02/57P03 now
  classify as completion-unknown.
- `SchemaTenantMigrationOrchestrator` recorded `MigrateResult`'s target
  version, which is empty for a tenant already current, reporting migrated
  tenants as unmigrated during a partial rollout. It now reads the applied
  version back from the tenant's schema history.
- `JpaStreamExecutor` checked only the declared return type for reactive
  publishers, and `RegisteredPostgreSqlCopyLoader` passed the COPY timeout
  to `SET`, which is parsed before parameter binding.

`JpaModuleBoundaryTest` enforces the plan's module map as package rules;
`verifyCleanArchitectureDependencies` governs edges between leaves and
cannot see these. Its first assertion is that the import is non-empty,
because every rule under it is a `noClasses()` rule and would pass
vacuously on an empty import.

Verified: 128 container tests across all seven lanes, 1183 unit tests,
`:adapter:outbound:persistence-jpa:check`, `:app-bootstrap:check`,
`verifyCleanArchitectureDependencies`, `verifyOneTypePerFile`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/jpa/observability.md

@@ -0,0 +1,61 @@
+# Observability
+
+Design §37. What is measured, and what must never appear in a measurement.
+
+## Bounded tags, always
+
+Every JPA metric carries exactly five tags: persistence unit, operation, query, outcome, failure
+category. All five are registered identifiers, validated by `LowCardinality` at construction rather
+than at the registry — so an unbounded value fails where it was introduced instead of surviving
+until a dashboard stops loading.
+
+Never a tag: entity id, tenant id, SQL parameter, exception message, JDBC URL. Each is unbounded, so
+each creates a time series per row or per failure; several are also the data the platform keeps out
+of logs, which a metrics backend would store just as durably and export just as widely.
+
+## Transaction metrics
+
+| Meter | Why it exists |
+|---|---|
+| `jpa.transaction.duration` | the baseline |
+| `jpa.transaction.rollback` | rollback rate by failure category |
+| `jpa.transaction.timeout` | timeouts, distinct from other rollbacks |
+| `jpa.transaction.completion.unknown` | its own counter, deliberately |
+
+Completion-unknown gets a separate counter rather than being folded into failures. It is the one
+outcome that means a human has to look: every other failure is a transaction that definitely did not
+happen, while this one is a transaction that may have.
+
+## Query metrics
+
+`jpa.query.duration` and `jpa.query.rows`. Rows are measured as well as duration because a query
+that issues one statement and hydrates twenty thousand rows is fast per statement and catastrophic
+per request — a duration metric alone reports it as merely slow.
+
+## Retry metrics
+
+Attempts are metrics, not warnings. Optimistic conflicts and serialization failures are the expected
+cost of concurrency; logging each at WARN pages someone for a system working as designed, after
+which the retry log gets filtered out and takes the genuinely interesting entries with it.
+
+`jpa.retry.attempt`, `jpa.retry.attempts` (distribution per operation), `jpa.retry.exhausted`.
+
+## Query names in SQL
+
+`NamedStatementInspector` prefixes each statement with its registered query name as a SQL comment,
+which travels into `pg_stat_activity`, `auto_explain`, and the slow-query log. Without it, "which
+endpoint issues this query" is answered by grepping the codebase for fragments of SQL.
+
+## Diagnostics
+
+`SqlDiagnosticRedactor` removes string literals, numbers, and anything email-shaped before SQL
+reaches a log. Redaction is blunt on purpose: preserving "harmless" values would require knowing
+which columns hold personal data.
+
+## The actuator endpoint
+
+`jpaplatform` reports database major version, provider version, schema version, OSIV state, runtime
+role verification, and capability levels. It reports no JDBC URL, no username, no SQL, and no entity
+catalog — an actuator endpoint is reachable by anyone who reaches the management port, and each of
+those would be a free reconnaissance answer. It is read-only: an endpoint that could trigger a
+migration or a repair would be an admin capability exposed over HTTP.