Persist destination recovery state across save and reopen

[Ankit6149]

Advances #29 with the missing canonical persistence boundary.

Implemented:

• Campaign now persists an allowlisted per-destination lifecycle/recovery state independently from content drafts
• contentful ChannelDraft records also carry the same safe recovery projection
• persists quality status, safe issue text/codes, retry count, failure class, quality-risk acceptance, and safe ProviderError metadata
• raw provider response bodies, arbitrary error fields, credentials, prompts and secret-like values are excluded from the recovery projection
• destinations that fail before producing text remain represented in Campaign.channels + Campaign.channelStates without fabricating an empty DraftRevision
• campaign reopen reconstructs the full safe channel recovery state and generation_status
• archive channel-state normalization uses the same safe projection
• save/reopen regression proves failed empty destination recovery survives while successful destinations remain intact

This does not claim durable in-flight generation resume across browser/server restart; that remains separate from completed/failed campaign persistence.

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