L3: attach body-internal comments to statement nodes

[sinha108]

Problem

v2 attaches each comment to exactly one node — the declaration it documents — which fixes v1's duplication (v1 used getAllContainedComments(), repeating a method's comment onto its type and compilation unit: a 2.09x factor on spring-petclinic). But comments inside method bodies have no declaration to attach to, so they are absent from the tree entirely. Measured at roughly 47 distinct comments per application (docs/design/notes/l1-v1-v2-comparison.md).

They remain recoverable from module.source, but they are not addressable or queryable — which matters for doc-driven and LLM consumers.

Scope boundary

Attaching body-internal comments to the statement nodes that L3 introduces. Depends on #183 (L3 populates body with statements); there is no node to attach them to before that. Does not revisit declaration comments, which are already correct.

Goals

• Attach each body-internal comment to the statement node it precedes (or is trailing on)
• Decide and record the shape: a comments list on the body node, consistent with declaration nodes
• Comments in a callable with no statements (e.g. an empty body) still have a home, or are documented as intentionally dropped
• Re-run the v1/v2 comparison and confirm the comment delta closes to duplication-only

Caveats and known risks

• Attachment is heuristic: JavaParser associates a comment with the following node, but a trailing end-of-line comment belongs to the preceding one. Pick a rule and document it.
• Do not reintroduce v1's duplication: a comment must appear on exactly one node.

Definition of done

• The comparison report's comment delta is explained entirely by v1 duplication, with no distinct comment missing from v2.