docs: introduce LingTai ANATOMY+CONTRACT navigation and interface system

[huangzesen]

Summary

Introduces the LingTai kernel's distributed code navigation (ANATOMY) and interface definition (CONTRACT) system into this repo, adapted to its size.

The repo already had three hand-written ANATOMY.md files in an ad-hoc shape. This PR rewrites them to the canonical LingTai convention and completes the paired system: a root contract-of-contract, three governed component contracts, and a mechanical drift checker + architecture-document validation suite.

What changed

• Root ANATOMY.md — rewritten with YAML frontmatter (related_files + maintenance), navigation model, five-section body, link/pairing semantics, and verified file:line citations throughout.
• Root CONTRACT.md (NEW) — the contract-of-contract: design principles (artifact-first responses, source_type dispatch, backend port isolation, packaged-skills-as-capability, thin wrappers), Core/Ports/Adapters architecture foundation, governed-component list, child template + pairing/ownership/versioning rules.
• src/spedas_agent_kit/ANATOMY.md — rewritten to convention; stale workflow citations corrected (search_data_sources 816→824, compare_sources 848→856, plan_observation 870→1170, create_analysis_bundle 1016→1351) and previously-uncited anchors added (_normalize_source_type server.py:1852, _wrap_data_payload :1927, serve() :2796, etc.).
• src/spedas_agent_kit/CONTRACT.md (NEW) — the package facade contract: the 13 base + 8 compat MCP tool surface, artifact-first {status, file_path, stats} response shape, structured-error contract, source_type dispatch, lazy backend imports.
• src/spedas_agent_kit/backends/ — ANATOMY.md rewritten; CONTRACT.md (NEW) defines the vendored CDAWeb/PDS/SPICE data-backend Port contract.
• src/spedas_agent_kit/resources/ — ANATOMY.md + CONTRACT.md (NEW) for the packaged-skills capability: skill catalog, event presets, provenance, schemas, index rendering.
• scripts/check_anatomy_drift.py (NEW) — adapted from the LingTai kernel drift checker: stdlib-only citation-rot scanner over every ANATOMY.md; report mode + --check gate for CI.
• tests/test_architecture_documents.py (NEW) — validates frontmatter, repo-relative dup-free related_files, reciprocal ANATOMY/CONTRACT pairing, root CONTRACT listing each governed child exactly once, child root_contract + paired anatomy, and no empty stub sections. Minimal frontmatter parser — no PyYAML dependency.

Validation

• tests/test_architecture_documents.py: 11 passed.
• scripts/check_anatomy_drift.py --check: zero drift across 4 ANATOMY files.
• Existing test_server/test_resources/test_config: untouched by this doc-only change (pre-existing spiceypy env gap unrelated to this PR).

Notes

• This is docs/governance only — no runtime code behavior changes.
• Component anatomy line counts (118–134) exceed the nominal ~80 guidance because the mandated verified-citation coverage for this three-backend facade needs room; the kernel's own root anatomy is 299 lines under the root-as-exception rule.