Add Hook Examples

[j-d-ha]

Priority: P1 - Critical
Tier: 2 - Single-Table Support
Effort: Medium (4-6 hours)

Already In Codebase

• There are example projects under examples/:
  • examples/DynamoMapper.SimpleExample
  • examples/DynamoMapper.FieldLevelOverride

Goal

Add example(s) demonstrating lifecycle hooks for single-table DynamoDB patterns.

Note: Hook code generation + tests are handled in #16. This story is examples-only.

Scope

• Add at least one example project showing:
  • pk/sk composition
  • a discriminator or type marker
  • optional TTL
  • optionally an “attribute bag” pattern

Acceptance criteria

• Example builds.
• Example compiles without manual edits to generated code.
• README/docs can link to it.