fix(docreader): make DOCX header extraction optional

[helloxjade]

Description

DOCX parsing currently returns only body content, so text that appears in a document header cannot be retrieved. Add an opt-in docx_include_headers parser rule for the builtin and MarkItDown engines, exposed in knowledge-base parser settings and the upload confirmation dialog. The default remains disabled.

When enabled, parsing prepends header text and tables, includes active first-page and even-page headers, and extracts inherited header parts only once. The python-docx fallback also honors the option. The option covers text and tables; header images and external AnyDoc processing are outside its supported extraction behavior.

Type of Change

• 🐛 Bug fix
• 🧪 Test
• 📚 Documentation update

Related Issue

Fixes #3849

Testing

• Reproduced missing header text in the builtin and MarkItDown paths with an in-memory DOCX before the fix.
• python -m unittest docreader.tests.test_docx_headers docreader.tests.test_docx_tables docreader.tests.test_docx_merge -q — 25 tests passed.
• go test ./internal/application/service -run 'TestApplyParserRuleOverrides|TestResolveProcessConfig' -count=1 — passed.
• npm test -- src/views/knowledge/settings/KBParserSettings.test.ts src/views/knowledge/components/UploadConfirmDialog.test.ts src/i18n/localeKeyAudit.test.ts — 22 tests passed.
• npm run type-check and npm run build — passed.
• Browser check of the actual parser-settings component with fixture engine resources: checkbox initially unchecked; clicking it emits the DOCX rule with docx_include_headers: true.
• git diff --check upstream/main...HEAD — passed (upstream is Tencent/WeKnora).
• golangci-lint run --new-from-rev=upstream/main ./... could not run because golangci-lint is not installed. The full-repository maintainer gate was not run; validation was scoped to the changed components.

Checklist

• Diff whitespace check passes against upstream main
• Changed source files are formatted
• Targeted tests for the changed packages/components pass
• Diff-scoped lint passes where applicable (tool unavailable; see above)
• Full-repository check limitations documented above
• Self-reviewed the code
• Added/updated tests covering the change
• Updated related documentation

Screenshots / Recordings

Actual KBParserSettings component, rendered with fixture parser engines: