Add static explainability snapshots and views

[xtraid]

Summary

• export closed, versioned snapshots for the parsed formula, canonical Wang tileset, and native-built region, connected by a SHA-256-bound manifest
• render formula, tileset sheet, and unassigned region snapshots in square or verified square-to-hex form
• add opt-in explainability styling to final solution renders, including colored edge bands, labels, boundary emphasis, and legends
• document the stage boundaries and add deterministic fixtures and pixel-stable golden images

Correctness boundaries

• the exporter uses the real parser and native region builder; the renderer consumes only JSON snapshots
• renderer modules do not import the solver, Z3, or private C structures
• the hex presentation reuses the pure port and independent checker introduced in T87
• default square and hex solution rendering is unchanged unless --explain is selected
• no C source, public C header, Makefile, dependency, lockfile, workflow, or solution schema changed
• detailed builder provenance, solver trace/GIF replay, and the optional technical report remain separate T89-T91 packets

Verification

• make check: 16 C binaries, 108 Python tests, native and cross-engine smoke
• renderer suite: 234 passed, including all 144 imported legacy tests
• Pages checker: 23 documents
• strict GCC and Clang builds
• ASan/UBSan/LSan and GCC analyzer
• git diff --check, JSON parsing, secret scan, artifact cleanup

Cachegrind was intentionally skipped because this packet changes no C or performance-sensitive core path. The local Memcheck pass covered 15 paths without findings before the final expensive witness case was stopped; CI remains authoritative for the required dynamic-analysis job.