feat(ui): add Rust leaderboard rank alert to course completion

[rohitpaulk]

Replace the generic info alert with a custom RoadmapInfoAlert component
showing the user's Rust leaderboard rank. Animate rank appearance with a fade
transition and loading placeholder. This improves feedback on course
progression by highlighting leaderboard status in a visually distinct alert.

---

This is part 2 of 2 in a stack made with GitButler:

•  2  feat(ui): add Rust leaderboard rank alert to course completion #3102 👈
•  1  feat(roadmap): always show RoadmapInfoAlert on all screen sizes #3101

[github-actions]

Test Results

  1 files  ±0    1 suites  ±0   9m 5s ⏱️ - 4m 21s
661 tests ±0  610 ✅  - 2  48 💤 ±0  0 ❌ ±0  3 🔥 +2 
661 runs  ±0  607 ✅  - 4  48 💤 ±0  3 ❌ +2  3 🔥 +2 

For more details on these errors, see this check.

Results for commit 7e2990a. ± Comparison against base commit d5d92f3.

♻️ This comment has been updated with latest results.

[codecov]

❌ 3 Tests Failed:

Tests completed	Failed	Passed	Skipped
613	3	610	48

View the top 3 failed test(s) by shortest run time

Chrome 140.0::Acceptance | course-page | attempt-course-stage: can pass course stage

Stack Traces | 2.71s run time

Promise rejected during "can pass course stage": Element not found.

PageObject: 'page.currentStepCompleteModal.completionMessage'
  Selector: '[data-test-current-step-complete-modal] [data-test-completion-message]'

Chrome 140.0::Acceptance | course-page | submit-course-stage-feedback: can submit course stage feedback after passing course stage

Stack Traces | 3.04s run time

completion text is stage completed

Chrome 140.0::Acceptance | course-page | view-course-stages-test: can view previous stages after completing them

Stack Traces | 3.16s run time

Promise rejected during "can view previous stages after completing them": Element not found.

PageObject: 'page.currentStepCompleteModal.completionMessage'
  Selector: '[data-test-current-step-complete-modal] [data-test-completion-message]'

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[codecov]

Bundle Report

Changes will increase total bundle size by 1.91kB (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
client-array-push	38.56MB	1.91kB (0.0%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/chunk.*.js	-6 bytes	398.31kB	-0.0%
assets/chunk.*.js	1.11kB	3.18MB	0.03%
assets/chunk.*.css	803 bytes	242.65kB	0.33%