Implemented progress overlay for IssueGraphWidget. ## Changes Made - **src/trckr_plow/tui/widgets.py:296-474**: Enhanced IssueGraphWidget with progress overlay - Added `_current_issue_start` attribute to track when current issue processing began - Added `_format_duration()` helper method to format seconds as "Xm Ys" format - Updated `render()` to include current issue ID and running time in header - Updated `update_state()` to track new issues and use `round_started_at` from workflow state - Updated `set_current()` to start timing when a new issue is set ## Display Format The progress overlay now shows: ``` Progress: 3/8 (37%) │ Elapsed: 12m 30s │ ETA: ~20m │ Current: PLOW-16 [2m 15s] ``` ## Tests Added (8 new tests) - `test_current_issue_timing`: Verifies current issue and timing display in header - `test_current_issue_timing_clears_on_completion`: Verifies timing clears on issue completion - `test_format_duration_*`: Tests duration formatting (0s, 30s, 1m, 1m 5s, 12m 34s) - `test_set_current_starts_timing`: Tests that set_current starts timing - `test_set_current_none_clears_timing`: Tests that set_current(None) clears timing - `test_update_state_uses_round_started_at`: Tests integration with WorkflowState ## Verification - All 586 tests pass - Lint passes (ruff check) - Coverage at 96% for tui/widgets.py