fix(inbound): derive emailId and receivedAt from the raw object so retries are idempotent (#202)

* fix(inbound): derive emailId and receivedAt from the raw object so retries are idempotent

The inbound Lambda minted a random emailId and a fresh receivedAt on every
invocation, so a Lambda async retry (for example after a PutEvents rejection)
re-parsed the same raw object under a new id, leaving a duplicate
parsed/{emailId}.json and a duplicate email.received event.

Derive emailId from a sha256 of the raw S3 key and receivedAt from the S3
record eventTime (falling back to now when absent).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LXhsBcDrKD8BtN1jaAyhD

* chore(inbound): rebuild inbound-processor bundle

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019LXhsBcDrKD8BtN1jaAyhD

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Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: stewartjarod