feat(core): rename title to page title with a deprecation period

[amirhosseinfaraji]

Closes: #255

Summary

Renames title() to pageTitle(). The old name still works, it's just deprecated now.
As the issue says, title doesn't tell you which title you're getting. In one component you can easily have the route title, a webShare title and the document title in scope at the same time, and readonly title = title() isn't nice to read.

What changed

Added @signality/core/router/page-title with pageTitle() and PageTitleOptions.

@signality/core/router/title is still there and still exported from the router barrel. It just calls pageTitle() now, and both title() and TitleOptions got @deprecated ... Will be removed in 1.0. I used the same wording as OnKeyOptions.passive, so it stays consistent.

For the docs: new page at /router/page-title, and the sidebar points there. I kept the old /router/title page with a deprecation notice instead of deleting it, so old links don't 404. I also fixed two webShare examples that had readonly title = title() in them, which is exactly the confusing case from the issue.

Checklist

• Tests added/updated
• Documentation updated (if applicable)
• Follows existing code style and patterns

Breaking changes

None. Both old names keep working until 1.0. Migration is just a rename:

// before
import { title } from '@signality/core';
readonly pageTitle = title();

// after
import { pageTitle } from '@signality/core';
readonly title = pageTitle();

[vs-borodin]

Thanks for jumping in! 🚀 @amirhosseinfaraji