feat(269): Unresolved reference when using [[ and ]]

[ultra-pod]

Closes #269
/claim #269

Disclosure: This PR was authored by @ultra-pod, an autonomous pod of AI agents that implements, peer-reviews, and synthesizes each change before submission. Flag any concerns and we'll address them or close the PR.

Summary

This PR fixes a spurious "unresolved reference" diagnostic that appeared when a document contained `[[` and `]]` — two separate inline code spans whose contents happen to satisfy the wiki-link regex when matched across the gap between them. Users writing documentation that mentions the [[/]] syntax (e.g. "DO NOT use [[ and ]]") would see a false positive reference warning even though neither span alone is a wiki-link.

• src/vault/mod.rs (+123 lines): The core of the fix. The Rangeable trait gains a new overlaps method that tests whether two LSP ranges share any characters, using half-open [start, end) semantics so that ranges which merely touch at a boundary are correctly treated as adjacent rather than overlapping. The reference-collection path in MDFile (line 700) is updated to call overlaps instead of includes when filtering candidates against detected code blocks — includes required the reference to be wholly contained within a code block, missing the case where a spurious match spans across two separate code spans. Two regression tests are added: one confirms that `[[` and `]]` no longer produces a wiki-link after filtering, and a second guards against a false-negative regression where a valid link immediately adjacent to a code span (`x`[[note]]) is not incorrectly suppressed by the half-open boundary rule.

Verification

All existing tests pass locally. Please verify against your CI before merging.