Add CONTRIBUTING.md and fix persona list in getting started guide

- Create contribution guide with bug reporting, PR guidelines, and
  code of conduct focused on therapeutic safety
- Fix incomplete persona list to show all 5 styles: warm & supportive,
  warm 4o-style, direct & challenging, coach, grounded & real

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/sample-session-notes.md

@@ -1,18 +0,0 @@
-# Session: January 15, 2025
-
-## Key Themes
-- Work overwhelm and difficulty setting boundaries
-- Fear of being seen as "not a team player"
-- Connection between self-worth and productivity
-
-## Emotional State
-- Exhausted, anxious when discussing boundaries
-- Some relief in naming the pattern
-
-## Patterns Noted
-- People-pleasing at cost of own wellbeing
-- Worth tied to capacity/output (likely early origin)
-
-## Threads to Revisit
-- Origin of "worth = what I can handle" belief
-- Small boundary experiment for next week