Update README to reflect current implementation state

[Copilot]

The README was describing Repstack as a project with mostly planned/unimplemented features, while the app is actually fully functional with workout logging, mesocycle planning, progress analytics, and PWA support all shipped.

Changes

Features section

• Renamed "Planned Features" → "Features"; marked all implemented items [x]
• Only remaining unchecked item: exercise substitution recommendations

Available Scripts

• Added missing test commands: test, test:run, test:coverage, test:e2e

Project Structure

• Replaced non-existent directories (features/, pages/, styles/) with actual layout
• Added e2e/, docs/, screenshots/, types/, test/
• Listed actual component subdirectories (exercises/, mesocycles/, workouts/, etc.)

Database Schema

• Expanded from 4 → 6 tables: added workoutSets and trainingSessions with descriptions

Project Status

• Updated from "Foundation Complete → Building Core Features" to reflect actual shipped state (16 implemented items listed)

Roadmap

• Replaced time-estimate phases with completed/in-progress status

Documentation

• Replaced "coming soon" placeholder with links to the 4 existing docs files (ARCHITECTURE.md, OFFLINE_FUNCTIONALITY.md, ACCESSIBILITY.md, TESTING.md)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update Readme</issue_title>
<issue_description>Update the readme</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update Readme #83

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