feat(export): compose inherited corpus projections

[tcballard]

Summary

• compose viewer, documents, and graph exports from the central retained catalog so inherited and overridden parent history is included by default
• add per-record source/layer/pin and complete override provenance, plus source-aware relationship and graph endpoints, through the published additive schemas
• add --local-only only to the three approved human export projections; OKF remains an explicitly local projection and MCP/enforcement gain no bypass
• preserve source-qualified identity and canonical override redirects in the embedded Portal, including same-canonical-ID parent/replacement records
• keep the prerequisite Portal shell byte-exact for no-manifest repositories and select the source-aware shell only for a composed export
• fail closed before HTML or OKF writes whose nonexistent, ..-containing, or symlinked target resolves inside the read-only parent materialisation
• reject conflicting repeated source identity deterministically and preserve exact captured inherited bytes

Stack

• depends on feat(mcp): serve verified federated corpora #459
• next: opt-in parent setup guidance and end-to-end certification

Closes #272

Validation

• federated export emission: 7/7
• export source identity: 6/6
• federation loader: 12/12
• OKF v0.2: 2/2
• decided CLI: 12/12
• export schema contracts: fixture, sample, live corpus, checkout stability, and federation cases conform
• Portal Vitest: 18/18
• Portal production and single-file viewer builds
• cargo clippy -p asdecided-core -p decided --all-targets -- -D warnings
• no-manifest viewer/documents/graph parity and frozen legacy HTML shell hash
• git diff --check

All listed checks pass.