Preference tool & UX

**Goal**:

- Read, write & list preferences
- Allow preferences to be read from other clients (IDE, etc).
- ~Sync across devices and Amazon Q surfaces~

**User story:**
Allow users to configure preferences ("I prefer short responses") and give directions ("always use yarn rather than npm") to the model.

**Proposed Implementation:**
- [] Add preferences tool that writes to a well-known file (for instance, `$AMAZONQ/preferences.yml`)
- [] Include well-known file in global context

**Open Question:**
- Should we make a generic context management tool or is there value in having one dedicated to storing user preferences?