refactor(pipeline): PR#7 slice 5 -- extract modules.rs (issue #67 hotspot split)

Wave 1 slice 5 (docs/plans/2026-08-19-evidence-architecture-execution-plan.md
Part E): move-only extraction of import-target resolution out of pipeline.rs
into pipeline/modules.rs. Moved: resolve_import_targets,
resolve_rust_module, resolve_candidates, resolve_module_to_path,
strip_js_emit_extension, own_module_dir, python_package_root, parent_of,
join_rel, normalize_rel -- the full Rust-crate-map/JS-relative/Python-
package/PHP-PSR-4/C#-namespace/JVM-package/Go-stdlib import resolution
cluster.

resolve_import_targets is pub(super) so rebuild_graph/incremental_graph_update
(both still in pipeline.rs) keep working unchanged, verified via callers()
before the move. The other nine functions stay plain private -- grepped
before the move to confirm none of their names appear anywhere else in
pipeline.rs, so they're called only within this cluster. ResolutionMaps
stays defined in pipeline.rs (already pub, not moved).

Zero net logic diff: every function body is byte-identical to its pre-move
form, confirmed via edit_lines' zero-hash preview mode before applying.

Verified: cargo build + clippy (calm-core, --all-features, --all-targets)
clean, zero warnings. Full test suite 1306 passed/0 failed.
golden_graph_equivalence's continued-vs-fresh mutation-round tests both pass.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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