feat: add SourceMap and canonical mapped Workshop artifact

[e54-bot]

Fixes #272

Summary

• Shape guard: attached mappings record the program shape; span accessors return None after rules, conditions, or actions are inserted or removed.
• Public SourceMap (extract / apply) and MappedText, defining workshop-rs/mapped-text-v1 (JSON: text, file table, shape, position-keyed spans). workshop-rs/text-v1 is plain Workshop text.
• apply rejects the whole mapping with a typed SourceMapError on shape mismatch or invalid entries; the program is left unchanged.
• Documented in docs/source-preservation.md, docs/compatibility-facades.md, and rustdoc.

Notes

• Shape also includes global/player variable and subroutine counts (ADR lists rules/conditions/actions) so declaration spans cannot displace.
• File table carries paths only; authored source text can be added later as an optional field.
• Re-attaching a span records the current shape of that scope.

Test plan

• cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --all-targets (real-project extract → emit → parse → apply round trip, shape mismatch, drift, non-ASCII columns)
• workshop-catalog-gen check, git diff --check
• cargo semver-checks: additive