[R1-03] Verify and finish inline citation click-through

[dkritarth]

Outcome

Inline numeric citations in supported PDFs navigate to correct reference and show useful reference context without breaking selection/highlights.

Dependencies

Blocked by #30. Existing PR #23 is stacked on PR #22 and must remain ordered.

Scope

Review PR #23 on top of merged highlight behavior. Validate citation parsing against multiple real paper layouts, tooltip accessibility, navigation, performance bounds, and highlight interoperability.

Acceptance criteria

• Supported single, list, range, and mixed markers resolve correctly.
• Click jumps to correct reference and gives visible feedback.
• Hover/focus exposes reference text accessibly.
• Missing/non-numeric/author-year references degrade inertly.
• Malformed huge ranges cannot hang renderer.
• Citation wrapping does not alter highlight anchor offsets.
• Search, selection, and text copy remain usable.
• Behavior verified on at least two real PDFs with different reference layouts.

Live verification

For each paper, test early/middle/late citations, list/range form, keyboard focus, tooltip, back-to-reading usability, existing highlights, and console.

Required PR evidence

PR must use Closes #31, stay focused, and include:

• regression/failing test or reproducible baseline;
• focused tests plus npm test, npm run typecheck, npm run build, git diff --check;
• exact Electron clicks/typing and observed result;
• screenshots for UI changes when tooling permits;
• console output, restart/persistence result, and unresolved limitations;
• real-paper evidence for reader behavior.

Existing PR code and mocked tests are not sufficient. Reviewer must independently exercise live flow before merge.