docs: add project progress tracker template guide

[annieappflowy]

Readers looking for a project progress tracker can now follow a complete guide from individual task updates to project-level counts and completion percentages. The article links to the live official template and both published databases, and explains the actual Status and Tags rollup settings, OR matching, the denominator, and empty-project behavior.

The guide targets non-branded searches such as “project progress tracker template” and “project completion percentage.” It includes three product screenshots, descriptive image text, concise search metadata, a worked example, troubleshooting, and an incoming link from the existing database task-management article. It is approximately 1,450 words, within a ten-minute read.

Live template: https://appflowy.com/templates/project-management/89d52779-0a6a-4fe9-a42d-611821eefea9

Article route: /blog/project-progress-tracker-template

Validation:

• Synced with main (912cef9) in a dedicated worktree.
• Current branch passed blog taxonomy, cached sitemap reproducibility, SEO publishing, template canonical URL regressions, lint, TypeScript, and diff checks.
• Full production build and Cypress coverage run in CI for the updated branch.
• Initial content validation included a passing production build with blog taxonomy, sitemap SEO validation, type checking, and linting.
• Production preview checked at desktop (1440px) and mobile (390px): correct title, description and canonical URL; screenshots load; template links present; no horizontal page overflow. Local preview requests for the configured production asset prefix were routed to the local build.
• Both public database previews checked anonymously. Copying the main template created both linked databases and preserved the expected rollup results; the temporary copy was moved to trash afterward.

The official template has AppFlowy as creator and Project Management saved as primary. This branch includes the primary-category canonical URL handling from #161 through its merge of main.

PR Checklist

• This PR contains documentation/content changes only.
• Production build and targeted preview checks passed.
• Full unrelated application test suites were not run locally.