[dmealing]

Fixes #527

What this does

Two providers can no longer register the same attribute name on one node type. The registry now records which provider registered each attribute and refuses a second provider's claim at composition, in all five ports (TypeScript, Python, C#, Java, Kotlin).

• A name another provider already holds on the same (type, subType) keeps ERR_PROVIDER_ATTR_CONFLICT. Its message now names the owning provider.
• A name another provider holds on the shared <type>.base root, or on a subtype of it, is the new ERR_PROVIDER_ATTR_SHADOW. This is checked in both directions, so registration order does not matter.
• A common attribute (accepted on every node type) is checked against other providers' common attributes and against per-type attributes, in both orders.
• A refusal names both providers and the attribute, and leaves nothing behind in the registry.
• Still allowed: the same provider repeating its own name, sibling subtypes sharing a name, and registration outside any provider.
• meta types --detail prints the registering provider next to each attribute, and its JSON output has a provider field.

This is how per-paradigm physical-name words (@column, @field) stay safe as providers multiply (ADR-0007, ADR-0018). No wire-name attribute is added.

Notes for review

• Core audit: the shipped core providers had no cross-provider collision in TypeScript, Python or C#. In Java, several providers re-declared @description per type next to the documentation provider's common one. Those per-type entries duplicated the common one (same type, same meaning), so they are removed and the common attribute is the single owner. @description is still accepted everywhere it was.
• Scope: the rule is scoped to one node type. Java chains every <type>.base to metadata.base; no other port has that edge, and treating it as a collision would make Java stricter than the rest.
• Java extend: a review finding showed Java's extendType accepted a name another provider owned on the inherited root. That is fixed, with a shared fixture so every port is held to it.
• ADR-0062 records the rule and the alternatives considered. docs/features/extending-with-providers.md, the authoring skill reference and the CHANGELOG (unreleased) are updated.
• New shared fixtures under fixtures/provider-composition-conformance/: attr-shadow-inherited, attr-shadow-descendant, the attr-ownership/ set, and the common-attribute cases for both orders.

Tests run

All on the rebased branch, serially:

• scripts/ci-local.sh --quick: passed
• TypeScript server suite: 13017 tests, 0 failures
• Python (without integration): 4102 passed
• C# conformance project: 2239 passed
• Java reactor (metadata, render, om, omdb, codegen-base/mustache/plantuml/spring, metadata-ktx, codegen-kotlin): build success, 0 failures

How it was validated

The no-mistakes gate ran twice. Run 1 passed review (two rounds of fixes), test, document and lint on this change, then failed at push because GitHub Git Operations was degraded. Run 2 was refused at push because it had skipped review and so had no review-approved head. Neither run published. The captain then approved pushing from the working copy after the full local suites above; the head matches what run 1 validated, rebased onto the latest main.