fix(web): handle malformed skill route params

[dirtybits]

Summary

• Treat malformed percent-encoded skill route parameters as unresolved instead of allowing decodeURIComponent to throw.
• Reject those parameters before database initialization for both canonical slug and legacy skill route resolution.
• Add a regression test proving malformed input returns null without issuing database work.

Test Plan

• npm run format:check
• npm run lint:web
• npm run typecheck
• npm test --workspace @agentvouch/web -- --maxWorkers=1 --no-fileParallelism (130 files, 954 tests)
• npm exec --workspace @agentvouch/web -- next build --webpack
• git diff --check origin/main...HEAD

Notes

• The production build completed successfully. It emitted its existing ox critical-dependency warning and expected local DATABASE_URL-absent snapshot fallback logs during static generation.