fix(web): New Session button on fresh start / no-opened-projects

[ndj888]

Problem

When you run opencode web for the first time (or with no persisted project state), the Web UI becomes unusable because:

1. Titlebar "New Session" button (＋): Clicking does nothing — the handler (openNewTab) falls through 5 cases and silently returns when none find a project directory.

2. Home page "New Session" buttons: Hidden entirely because newSessionProject() returns undefined when projects() (persisted opened-projects list) is empty.

The issue persists even though the server does have registered projects (returned by GET /project).

Root Cause

The web UI stores opened projects in localStorage (opencode.global.dat:server → projects.<scope>). On fresh start:

• global.servers.list() may be populated (via entry.tsx servers={[server]}), but
• global.ensureServerCtx(conn).projects.list() reads only persisted projects — which are empty on first launch.

The server-registered projects (from sync.data.project, populated by the /project API) are never consulted as a fallback for session creation.

Reproduce

opencode web --port 4096
# Open http://127.0.0.1:4096/
# Click "New Session"  →  nothing happens

Fix

Two targeted changes:

1. packages/app/src/pages/home.tsx — newSessionProject():

   • Add a final ?? focusedSync().data.project[0] fallback.
   • When no project is opened, picks the first server-registered project so the empty-state and in-list "New Session" buttons appear and work.

2. packages/app/src/components/titlebar.tsx — openNewTab():

   • After the 5-case fallback chain fails, add a Case 6 that reads global.ensureServerCtx(conn).sync.data.project[0].
   • Uses the server-registered projects as the last-resort directory for creating a new draft session.

Verification

Manually tested on opencode web --port 19820 with cleared localStorage:

• Page loads with server-registered project visible as the source for new sessions
• Titlebar "New Session" button navigates to /new-session?draftId=...
• Home page show "New Session" buttons in both the empty state and session list
• All API requests return HTTP 200

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