[snehmatic]

Closes #178

This PR adds the ability to pause and resume focus sessions.

Changes

• Updated the FocusSession model with PausedDuration and LastPausedAt to robustly track accumulated paused time without miscalculating ongoing durations.
• Added mindloop focus pause and mindloop focus resume CLI commands.
• Updated mindloop focus status to factor in paused duration and conditionally print ⏸ and Paused Focus: instead of Active Focus: when the session is parked.
• Created HTTP handlers HandleFocusPause and HandleFocusResume with HTMX partial rendering compatibility.
• Updated the frontend HTMX focus_active_timer.html block with Pause and Resume buttons based on the session's active status, and updated the JS interval timer to account for paused time.
• Updated docs/CLI_USAGE.md and docs/FEATURES.md.