UI improvements: responsive layout, unified panels, credit legend

- Add responsive 2-panel layout (mobile single-col, tablet/desktop grid)
- Unify specialization ranking with credit bars, status badges, and
  expandable allocation breakdowns (remove standalone ResultsDashboard)
- Inline decision tree ceiling data on course buttons with spec counts
- Add Clear All button to reset all course selections
- Add collapsible CreditLegend explaining bars, badges, and limits
- Extract ModeComparison and MutualExclusionWarnings to Notifications
- Add useMediaQuery hook with matchMedia-based breakpoint detection

openspec/changes/ui-improvements/specs/bulk-actions/spec.md

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+## ADDED Requirements
+
+### Requirement: Clear all course selections
+The course selection panel SHALL provide a "Clear All" button that resets all pinned course selections at once.
+
+#### Scenario: Clear all with some pinned
+- **WHEN** at least one course is pinned and the user clicks "Clear All"
+- **THEN** all pinned courses SHALL be unpinned and every elective set SHALL return to the open state showing all course options
+
+#### Scenario: Clear all button visibility
+- **WHEN** no courses are pinned
+- **THEN** the "Clear All" button SHALL not be visible
+
+#### Scenario: Clear all button visible
+- **WHEN** at least one course is pinned
+- **THEN** the "Clear All" button SHALL be visible in the course selection panel header
+
+### Requirement: State persistence after clear all
+After clearing all selections, the cleared state SHALL be persisted to localStorage like any other state change.
+
+#### Scenario: Persistence
+- **WHEN** the user clicks "Clear All" and reloads the page
+- **THEN** all sets SHALL remain in the open (unpinned) state