fix(calendar): make mobile calendar title fit

[keilogic]

Summary

• Use a compact mobile day-view title such as Sat, May 23, 2020 instead of the full weekday title.
• Replace the mobile calendar toolbar's width: 100% inline header with a flex-safe container so the menu button, previous/next buttons, and title can share the viewport width.
• Constrain the mobile toolbar title with nowrap/ellipsis so longer titles cannot push controls off-screen.
• Add a regression spec for the mobile day-view title.

Closes #575

Testing

• npm ci
• Pre-fix focused spec failed as expected with TS2339: Property 'mobileCalendarTitle' does not exist on type 'CalendarAppComponent'.
• npx ng test runbox7 --watch=false --browsers=FirefoxHeadless --include=src/app/calendar-app/calendar-app.component.spec.ts
• npx tsc -p src/tsconfig.app.json --noEmit
• npx tsc -p src/tsconfig.spec.json --noEmit
• npm run lint -- --quiet
• npm run policy (branch commits OK; existing historical upstream commit-message warnings remain)
• git diff --check origin/master...HEAD
• git show --check --stat --oneline HEAD
• PowerShell-native production sequence: SKIP_CHANGELOG=1, node src/build/pre-build.js, npx ng build --configuration production --base-href=/app/ runbox7, node src/build/post-build.js (existing Angular/CommonJS/theming warnings only; hash a0cd623a2e43ef64)

AI Disclosure

I used OpenAI Codex to inspect the issue and current source, make the code/test changes, and run the validation commands listed above.

[castaway]

lgtm