Eliminate remaining target-spine dependency back-edges

[devin-ai-integration]

Goal

Drive scripts/layering/back-edge-baseline.json toward zero in dependency-safe PRs. PR #1174 made
the exact identities down-only; this issue coordinates removal without a mass rewrite.

Current edge classes

• client -> daemon-client (1)
• commands -> cli (7)
• commands -> client (3)
• commands -> daemon-server (2)
• platforms -> core (16)
• platforms -> daemon-server (7)

Sequence

1. Move shared CLI flag/schema contracts below CLI; remove commands -> cli.
2. Move command-aware serializers/normalizers/contracts below the client projection; remove
   commands -> client.
3. Move selector-resolution contracts used by commands out of daemon-server.
4. Move request cancellation/progress and other neutral request primitives below daemon-server;
   remove platforms -> daemon-server.
5. Classify and invert platforms -> core by neutral contract family, one family per PR.
6. Remove the remaining client -> daemon-client edge or document a corrected target-layer name if
   the dependency is conceptually legal.

Each child PR must delete exact identities from the baseline and add or tighten the corresponding
layering rule. Do not regenerate or raise the baseline.

Constraints

• Preserve public imports and runtime behavior.
• Prefer neutral contract moves over wrappers or re-export barrels.
• Split large tests only when the source seam changes.
• Do not combine multiple edge classes in one PR.

Completion

• commands -> cli is zero
• commands -> client is zero
• commands -> daemon-server is zero
• platforms -> daemon-server is zero
• platforms -> core is zero or the target DAG is explicitly corrected by ADR
• client -> daemon-client is zero or the target DAG is explicitly corrected by ADR

Origin: post-#1174 architecture follow-up.

[devin-ai-integration]

Completed by #1210: all six ranked target-spine edge classes are zero. #1213 removes the now-empty debt baseline and enforces zero directly.