docs: add ADR for authorization schema source tracking

[rodmgwgu]

Problem

The authorization schema loading pipeline needs a documented decision record explaining how schema definitions and their source are tracked before the implementation lands.

Approach

Adds ADR 0025-authorization-schema-source-tracking.rst describing the source-tracking design.

AI Usage

Kiro was used to assist on research and write the ADR with human guidance and validation.

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Stack (1/3) — split from a single combined commit for reviewability:

1. This PR — ADR doc (base: main)
2. rod/authz-schema-files — authz schema YAML files (base: this branch)
3. rod/authz-schema-loader — schema loading pipeline (base: PR 2)

Merge checklist:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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