feat: prioritize active work and cache project layouts

[teloverge]

Summary

• add the viewer-aware work-priority hierarchy for doing now, owned next/future work, available work, team work, and closed issues
• keep active nodes visible at every zoom level while making traversed connections quiet except where they lead directly into active work
• preserve account-safe ownership across provider changes and serialize provider replacement with model/cache publication
• move first-time constellation layout work off the UI thread, show elapsed seconds with Cancel/Retry, restore the last charted project after cancellation or failure, and cache completed layouts for instant revisits

Why

The graph previously gave completed paths too much visual weight and did not distinguish the user's current, next, and future work strongly enough. Project changes also recomputed constellation layouts on the UI thread, making navigation appear stuck and allowing periodic model refreshes to restart an in-flight layout.

User impact

Users can identify their active work at a glance, retain semantic context for team and closed work, and switch projects immediately. First loads remain interactive and cancellable, failures restore the previous successful selection, and completed projects reopen from cache without another loading transition.

Validation

• vp exec vitest run --reporter=dot — 31 files, 265 tests passed
• vp run check — 0 errors and 0 warnings
• vp run build — production build emitted the layout worker bundle
• cargo.exe fmt --all -- --check
• cargo.exe clippy --workspace --all-targets --locked -- -D warnings
• cargo.exe test --workspace --locked -j 1
• browser acceptance on the rebuilt Windows dev server: stopwatch remained monotonic across refreshes, Cancel restored the last charted project, and cached Encrydle/Evolve revisits skipped loading

Closes #91
Closes #92
Closes #93
Closes #94
Closes #95
Closes #96