fix(wiki): skip ambiguous single-Han auto-links

[JYao-Chen]

Description

Wiki auto-linking currently treats a one-character Han page title as a safe substring match. Chinese prose has no whitespace token boundary, so a page such as 风 can be injected inside 风沙, and 目 inside 栏目, splitting normal words into incorrect links.

This change skips automatic cross-link injection when the surface form is exactly one Han character. It does not remove one-character Wiki pages and it preserves explicit [[slug|label]] links produced by the generator or author.

Regression tests cover both the false-positive substring and explicit-link preservation.

Type of Change

• 🐛 Bug fix
• 🧪 Test

Related Issue

N/A

Testing

• go test ./internal/application/service -run 'TestLinkifyContent|TestFindFirstSafeMatch|TestComputeForbiddenSpans' -count=1
• go vet ./internal/application/service
• git diff --check origin/main...HEAD

Checklist

• git diff --check origin/main...HEAD passes
• Changed source files are formatted
• Targeted tests for the changed packages/components pass
• Diff-scoped lint passes where applicable
• Full-repository checks were run, or any unrelated/environment-dependent failures are documented above
• Self-reviewed the code
• Added/updated tests covering the change
• Updated related documentation
• Breaking changes are clearly called out in the description above

Screenshots / Recordings

N/A