fix(align): strip field comments from both diff sides

[peczenyj]

Problem

In side-by-side (and unified) diff mode, the current column showed trailing/doc comments after field definitions while the proposed column omitted them — making a pure reordering look like it also deleted the field comments.

  current                                            │ proposed
  ───────────────────────────────────────────────────┼─────────────────────────
  type Layout struct {                               │ type Layout struct {
      TypeParams string // for a generic type ("[T]")│     TypeParams string
      Note       string // optional caveat shown ... │     Note       string

Root cause

Upstream fieldalignment deliberately clears each field's Doc/Comment when building the suggested-fix text (f.Comment = nil; f.Doc = nil, TODO golang/go#20744). structalign reads Original from raw source (comments intact) but takes Proposed straight from that comment-less fix text — hence the asymmetry.

Fix

Replace the conditional tag-strip with a single normalizeStruct(src, keepTags) helper applied to both sides. It drops per-field comments (by parsing without parser.ParseComments, so they never enter the AST) and clears tags only when -tags is unset. Both columns now go through the same reprint, so they stay symmetric and the diff shows only the reordering.

Verification

• New unit tests: TestNormalizeStructStripsComments, TestFindingsStripsCommentsFromBothSides, TestFindingsKeepTagsStillStripsComments (comments gone on both sides regardless of -tags; tags survive when -tags is set).
• Existing golden fixtures unchanged (the sample structs have no comments).
• task ci green; manually reproduced against pkg/common.Layout — both columns now comment-free.

Closes #88

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