refactor: consolidate POD service orchestration

[VPRamon]

Summary

The previous service layer mixed configuration validation, synthetic workflow setup, pipeline execution, artifact writing, and transport concerns. CLI and REST had to know pipeline details, while the public result exposed only a manifest path and failures surfaced as std::io::Error or pipeline errors.

This PR makes spod an application/service layer around Siderust:

• adds a high-level Runner / RunRequest / RunResult service boundary;
• introduces explicit Workflow, Artifacts, RunProvenance, and categorized ServiceError types;
• validates schema, workflow, forces, and unsupported real-data inputs before execution;
• routes both CLI and REST synthetic execution through the same runner;
• keeps the deterministic synthetic workflow as an explicit reference/integration workflow;
• keeps artifact layout and SP3, OEM, residual CSV, QC JSON, and manifest generation unchanged;
• documents the Siderust ownership boundary and the temporary local Vallado SGP4/SDP4 exception.

The configuration schema remains deliberately small. Unknown fields fail explicitly, workflow: synthetic is supported (and defaults for existing configs), and relative output directories resolve relative to the configuration file.

Deferred scope

This does not implement the full job lifecycle/persistence work planned for #11, real GNSS POD from #20, dataset acquisition from #21, mission profiles from #22, or Siderust SGP4/SDP4 parity (#29 / Siderust#98). Production scheduling, persistence, authentication, and new science remain out of scope.

Validation

• cargo fmt --all -- --check
• cargo check --locked --workspace --all-targets --all-features
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --no-fail-fast
• cargo test --workspace --no-default-features --no-fail-fast
• cargo test --workspace --all-features --no-fail-fast
• cargo test --doc --workspace --all-features
• cargo doc --workspace --no-deps
• bash scripts/check_dep_graph.sh
• bash scripts/check_no_todos.sh
• bash scripts/check_legacy_name_refs.sh
• cargo deny --all-features check (passes with existing duplicate-crate warning)
• cargo run --quiet --bin spod -- run examples/configs/leo_gnss_mvp1.yaml

Closes #10

[chatgpt-codex-connector]

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