Improve analysis UX: algorithm explanations, skeleton loading, auto-expand achieved specs

- Replace terse one-line optimization mode descriptions with clearer multi-sentence
  explanations of how Maximize Count and Priority Order algorithms behave
- Add skeleton loading placeholders on course buttons while analysis is pending
- Auto-expand achieved specializations to show credit breakdown by default
- Add instructional subtitles to Course Selection and Specializations sections
- Make Clear and Clear All buttons more prominent with visible backgrounds

openspec/changes/analysis-ux-improvements/specs/expanded-achieved-specializations/spec.md

@@ -0,0 +1,20 @@
+## ADDED Requirements
+
+### Requirement: Achieved specializations default to expanded
+The SpecializationRanking component SHALL initialize with all achieved specializations in the expanded state, showing their AllocationBreakdown credit list by default.
+
+#### Scenario: Initial render with achieved specializations
+- **WHEN** the SpecializationRanking component renders with one or more achieved specializations
+- **THEN** the AllocationBreakdown (per-course credit list) SHALL be visible for each achieved specialization without user interaction
+
+#### Scenario: Achieved set changes after course selection
+- **WHEN** the set of achieved specializations changes due to a course pin/unpin or ranking reorder
+- **THEN** all newly achieved specializations SHALL be expanded by default
+
+#### Scenario: User manually collapses an achieved specialization
+- **WHEN** the user clicks on an achieved specialization that is currently expanded
+- **THEN** the AllocationBreakdown for that specialization SHALL collapse
+
+#### Scenario: Non-achieved specializations remain non-expandable
+- **WHEN** a specialization has a status other than "achieved"
+- **THEN** it SHALL NOT display an AllocationBreakdown and SHALL NOT be expandable