fix(wiki): preserve graph and tenant integrity

[yangcongcong-coding]

Summary

• count graph links as distinct, live neighbors instead of raw in_links + out_links
• inherit the knowledge base tenant when a Wiki page is created without an explicit tenant_id
• add regression tests for both data-integrity issues

Root cause

Reciprocal Wiki links appear in both in_links and out_links. Adding both array lengths double-counts the same neighbor, while missing and self-referential targets are counted even though the graph cannot render them. This can make the sidebar report an unreachable or dead neighbor when every real neighbor is present.

The built-in Wiki fixer creates pages without setting TenantID. CreatePage previously persisted that zero value instead of resolving ownership from the parent knowledge base, leaving tenantless Wiki rows.

Impact

• graph neighbor totals match the distinct nodes that can actually be displayed
• reciprocal links no longer create false dead-link warnings
• Wiki fixer-created pages remain scoped to the knowledge base tenant

Validation

go test ./internal/application/service \
  -run 'Test(InheritWikiPageTenant|ComputeGraphSubset|ParseOutLinks)' \
  -count=1

ok github.com/Tencent/WeKnora/internal/application/service 0.278s

gofmt and git diff --check also pass.