Ignore wikilinks that overlap inline code spans

[6crucified]

/claim #269

Summary

• treat code spans and fenced code blocks as exclusions for any reference that overlaps them, not only references fully contained inside one code block
• add a regression test for the reported `[[` ... `]]` inline-code false positive
• add a control test showing a real wikilink outside inline code still parses normally

Why

The current wikilink regex can span from `[[` in one inline code span to `]]` in another. That produces a false unresolved reference because the match overlaps multiple code spans and is not filtered out by the existing containment check.

Validation

• cargo fmt --check
• git diff --check -- src/vault/mod.rs

Note: I attempted to run a focused cargo test for the new regression locally, but the first full test-binary build for this repo was unusually slow in this environment and did not complete within the time budget.