Web architecture improvements (epic)

Epic: Web architecture improvements for the Omni app.

Motivated by the Invest page build, which surfaced architectural gaps: duplicated CSS, untested pure logic, embedded JS without tooling, no shared component library for fund pages, and a deploy pipeline bug.

Work items (in priority order)

1. Unit tests for Omni/Fund/Invest.hs (t-XXX)

Write Omni/Fund/Invest/Test.hs covering pure functions: kellyOptimalN, computeDeltas, mkDelta, buildActuals, bucketize, boxMuller, buildAssetList, and JSON round-trips. Follow Omni/Fund/Overview/Test.hs pattern.

2. Fix deployer unit-file staleness bug (t-XXX)

The deployer compares store paths but doesn't detect when the systemd unit file on disk was manually edited to a different path. If the manifest says "already at X" but the running service has a different path in ExecStart, the deployer should still regenerate the unit file and restart.

3. Extract shared fund CSS into Omni/Fund/Web/Style.hs (t-XXX)

Move fund-kpi-grid, fund-section-block, fund-kpi, slider, delta-table CSS from Overview.hs and Invest.hs into a shared Clay module. Both pages import and reuse. Eliminates copy-paste drift (Overview has uppercase labels + 14px padding, Invest has 12px — pick one).

4. Extract shared fund Lucid components into Omni/Fund/Web/Components.hs (t-XXX)

renderKpi, renderKpiGrid, renderSection, renderSlider, renderDeltaTable. Update Overview.hs and Invest.hs to use them. Add HTML rendering tests.

5. Build component preview server (t-XXX)

A standalone Haskell web server that renders every shared component with dummy data on a single page. For design review. Buildable with bild Omni/Web/Preview.hs, runs on a local port.

6. Migrate Overview.hs page-local CSS from Text.unlines to Clay (t-XXX)

The Overview page has ~100 lines of CSS as raw strings. Convert to Clay for type checking and composability. Low-risk refactor since the page is read-only.

7. Web architecture conventions doc (done)

Written at Omni/Web/CONVENTIONS.md. Documents the three interactivity patterns, CSS architecture, component architecture, testing strategy, and JS strategy.