feat: Workout History Dashboard

[MaximumTrainer]

Summary

Add a local Workout History Dashboard tab to the main window that lists all completed workout sessions stored on disk, with summary statistics, trend charts, and drill-down per session.

Motivation

Users currently rely entirely on external platforms (Strava, TrainingPeaks, Intervals.icu) to review training history. A built-in history view provides instant offline access and keeps engagement inside the app.

Acceptance Criteria

• A History tab is present in the main window alongside Workouts and Courses
• The tab lists all FIT files in the configured history folder, sorted by date descending
• Each row shows: date, workout name, duration, TSS, normalised power, avg power, avg HR, total calories, total distance
• Clicking a row opens a detail pane with per-interval stats and the power/HR/cadence graph re-rendered from the FIT data
• A 30-day rolling TSS bar chart is displayed at the top of the History tab
• The list supports search and filter by workout name and date range
• Deleting a history entry prompts for confirmation before removing the FIT file from disk
• Consistent behaviour across all platforms; WASM reads from the in-memory virtual file system
• Unit tests cover FIT file indexing and TSS aggregation logic
• uses locally stored activties, not remote from intervals.icu