feat: demo recording, completion screen fixes and the nine-step cache-aside roadmap

[OthmaneZ05]

Summary of Changes

Lands the demo recording, three fixes found while recording it, and the recalibrated cache-aside roadmap.

• Demo GIF at docs/media/torollo-demo.gif (1280×720, 25 s, 1.4 MB), recorded against the real backend and real Docker: step 7 of Deploy a resilient three-tier app fails because the database still accepts 5432 from the load balancer, the security group is fixed, the step passes, the completion screen opens. The reproducible tooling lives in demo/ (plays the other steps through the API, records with Playwright, overlays the cursor, encodes with ffmpeg); demo/out/ and demo/node_modules/ are ignored.
• Modals render through a portal into document.body. At 720p the completion screen was drawn under the topbar and the project chip. The completion screen now lays out in two columns when there is room, so it fits a 1280×720 window without scrolling.
• The network audit no longer repeats an unchanged finding on every config save. Editing three firewall rules in a row used to toast the same warning three times.
• Cache-aside with Redis recalibrated to 9 steps and 45 min (EN and FR), with a new step, The cache goes dark: the store must survive a cache outage and come back on a hit.
• .claude/ added to .gitignore.

The README embed of the GIF comes in a follow-up PR together with a README refresh.

Types of Changes

• New feature / node type addition
• Bug fix (non-breaking change resolving an issue)
• Refactoring / structural cleanup
• Documentation update

Verification & Testing

Automated Checks

• Run npm run lint successfully with no errors (backend clean; frontend 0 errors, 5 pre-existing warnings in files this PR does not touch)
• Run npm run build successfully with no compilation errors (backend and frontend)
• Run npm test successfully (backend 481 passed; frontend 367 passed with --maxWorkers=1)
• npm run roadmap:validate OK on cache-aside-redis.json and cache-aside-redis.fr.json (9 steps each)

Manual Verification

• The GIF is the verification of the two UI fixes: recorded at 1280×720 against the real backend and real Docker, the completion screen is fully visible on top of the canvas chrome, and the "db in a public subnet" warning appears once while the rules are edited.
• Cache-aside, 9 steps: played fail→pass per step against real Docker through the validation API. Every step fails before the work with the expected message and passes after it; a full replay of all 9 steps stays green. The outage step observed served from database in 17105 ms while Redis was stopped, then a cache hit after the restart.

Checklist

• My code follows the repository's code style and lint standards
• I have updated the documentation or instructions if necessary
• All unit and integration tests are passing