* fix(popup): stabilize tabs and refine visual hierarchy

Reserve selected-label widths, align provider actions, and make popup header metadata and Spend sections consistent. Refresh the synthetic README screenshots and tour. Update usage guidance and Unreleased; no parity TODO or CLI contract changes.

* test(popup): cover provider tab selection widths

Address the CodeRabbit coverage suggestion by selecting each real inline provider tab in tabs-overflow and comparing all measured widths after every layout pass. The check rejects the original provider-label sizing. Document the smoke coverage; no additional behavior or parity TODO change.