Fix headless startup window minimization

[qayshp]

Summary

• Skip window minimization when headless startup intentionally has no BrowserWindow.
• Preserve the existing start-minimized behavior whenever a window is available.
• Add a focused regression check for the headless/null-window, disabled, and ordinary minimization paths.

Root cause

Headless mode returns from AppWindow.build() without creating a BrowserWindow. During server initialization, preChecks() still reads the independent start_minimized setting and unconditionally calls this.window.minimize(). When both settings are enabled, the null window dereference rejects startup before the HTTP server begins listening.

The minimization decision now goes through a small null-safe helper. This keeps the normal GUI behavior unchanged while making the headless combination a no-op.

User impact

BlueBubbles can start headlessly from SSH, a LaunchAgent, or another session without a WindowServer connection even when start_minimized remains enabled. Existing GUI launches with start-minimized enabled still minimize their window.

Validation

Passed:

• npm --workspace @bluebubbles/server run test:headless-window
• Prettier check for all changed files
• Targeted ESLint for src/server/index.ts and src/server/utils/WindowUtils.ts
• Targeted TypeScript --noEmit check for WindowUtils.ts
• git diff --check

The full repository checks still expose unrelated errors in unchanged origin/development files:

• Full server lint: existing max-len errors in src/server/api/privateApi/modes/dylibPlugins/index.ts lines 143 and 158.
• Production server build: existing NodeJS.Timer / clearInterval type mismatch in src/server/lib/ScheduledService.ts line 39.

Fixes #789.

Related: #733.

[qayshp]

Self-review: the null guard addresses the reported crash and the focused regression check covers both headless and ordinary window paths. I found one minor diagnostics follow-up to address before this draft is marked ready.

[qayshp]

Validation update

Validated on the current SIP-enabled Tahoe host:

• Passed: npm --workspace @bluebubbles/server run test:headless-window
• The focused check covers a null headless window, disabled start-minimized behavior, and ordinary window minimization.

A fresh live application startup was not completed. The normal production build remains blocked by the unrelated pre-existing ScheduledService.ts:39 NodeJS.Timer / clearInterval type error, so this result does not claim an end-to-end packaged-app pass.

[qayshp]

Latest-head validation (235ae213):

• Moved only the unchanged focused-test script entry to a distinct package.json anchor so this PR merges cleanly with the sibling Server PRs.
• Re-ran the focused check under Node 20: passed.
• Changed-file Prettier, targeted ESLint, full-server lint comparison, and git diff --check behaved as documented.
• The production build reaches only the unchanged ScheduledService.ts:39 type error already present on the base branch.
• A sequential merge simulation against current origin/development with Server Resolve Tahoe fallback service from chat metadata #832–Restore legacy macOS update manifest generation #834 completed without conflicts.