feat(web): add manual project visibility

[danieliser]

What Changed

Adds persisted, manual project visibility controls to both sidebar implementations:

• Right-click a visible project and choose Hide.
• Expand the ~~~ hidden (N) ~~~ shelf at the bottom and right-click a project to Show it again.
• Treat grouped project references as one visibility choice.
• Temporarily promote hidden projects with running or starting chats so active work cannot disappear.
• Keep hidden inactive projects lightweight by avoiding full project rows and per-project thread/detail subscriptions.

The V2 sidebar applies the same behavior in its project picker and filters hidden project threads before row mounting.

Why

Automatic sorting or hiding made the sidebar feel unpredictable. Explicit per-project control lets users decide what stays out of the active list while still protecting active chats from being hidden.

The collapsed shelf also reduces inactive sidebar work without pretending that all global project summary state can be removed.

UI Changes

Demo

Classic sidebar

Right-click to hide	Expand the hidden shelf and right-click to show

V2 project picker

Validation

• vp test run packages/contracts/src/settings.test.ts apps/web/src/components/Sidebar.logic.test.ts — 110 tests passed
• Contracts and web targeted typechecks
• Targeted lint and formatting checks
• Integrated browser verification in classic and V2 sidebars, including hidden-row suppression

Effective non-test diff: 323 changed lines (size:L, below XL).

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a GIF for the interaction flow

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