feat: add magazine publication profile

[szmyty]

Summary

• add a bundled, versioned magazine derivative profile using the generic artifact-forest planner
• add the renderflow.publication/v1 issue contract with layout, rights, accessibility, artwork, identifier, and per-role preflight policy
• support multiple named roles sharing one format render, so press/proof/screen outputs reuse the same DAG work when render configuration matches
• gate approved/released contracts on matching reviewed rights and publication-hygiene policy
• emit deterministic publication, artifact-manifest, provenance, preflight, and SHA-256 metadata sidecars
• integrate EPUB/KEPUB as ordinary optional profile targets and report unavailable branches honestly
• add a redistribution-safe synthetic magazine fixture, generated schema/reference updates, and end-to-end workflow docs

Verification

• cargo check --workspace --all-targets
• focused workspace lib/bin Clippy with the two pre-existing baseline lint allowances
• fixture spec validation
• full --profile magazine --dry-run artifact-forest smoke
• real HTML publication slice with JSON parsing and SHA-256 verification

Per the current sprint direction, the test suite was not run. MkDocs was unavailable in this environment.

Closes #364

[devactivity-app]

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