Fix white-screen crash: nullable bindings must say null

[alejandro-nexcade]

Root cause (systematic-debugging trace)

The app went white because React unmounted the tree on `TypeError: null is not an object (evaluating 'summary.total')` at `ci.ts:69` during board render. The chain:

1. serde serializes `Option::None` as `null` (key always present — no `skip_serializing_if`)
2. `#[ts(optional)]` generated `ci_summary?: CiSummary` — claiming absent-or-present, i.e. `undefined`, never `null`
3. so `ci === undefined ? "none" : ciState(ci)` type-checked while passing runtime `null` straight into `ciState`
4. test fixtures omitted the field (undefined), matching the wrong type — every suite green, runtime dead

Only reproducible with hydrated reviews (persisted state), which is why headless probes and CI never saw it.

Fix (the class, not the line)

• Removed `#[ts(optional)]` from the four always-present-null fields (`plan_path`, `dispatch_snapshot`, `ci_summary`, `last_reviewed_sha`); bindings now say `T | null` — the wire truth. tsc immediately surfaced every dishonest guard; all fixed.
• Fixtures now mirror the wire shape (`null`, not omitted) so tests exercise reality.
• Regression tests lock the null path (rank, fast lane, mixed board sort).

Verified

cargo test 458 · clippy -D warnings · tsc strict clean · vitest incl. new regressions · vite build.

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