feat(contracts): keep terminal campaign storage readable

[shinzoxD]

Summary

Once a campaign reaches a terminal state (Settled, Failed, Resolved), write paths stop calling extend_ttl on its persistent entries. After PERSISTENT_BUMP_AMOUNT (~90 days of ledgers) those keys archive and history becomes unreadable until a RestoreFootprintOp.

This adds a permissionless touch_campaign(campaign_id) on both contracts that only extends TTL (no other state change), so an indexer/keeper can cheaply keep settled history alive.

Public getters already return Option on master. Mutating paths that still require a live record now panic with an archival-aware message pointing at touch_campaign / RestoreFootprintOp.

Closes #154

Changes

ProductionEscrowContract

• touch_campaign bumps Campaign and, when present, Dispute, Tranches, HarvestRecord, plus instance TTL
• require_campaign / require_dispute replace opaque campaign/dispute-not-found panics
• Documented TTL constants, terminal keys, cadence, and restore path in production_escrow/README.md

RegistryContract

• touch_campaign bumps Campaign metadata, CampaignRecord, activity page-count and every activity page, plus instance TTL
• require_campaign_record panic mentions restore / touch
• New registry/README.md with the same TTL/archival ops notes

Contribution(id, investor) keys are per-investor and are not enumerated by touch_campaign (no on-chain investor index). Keep those alive via get_contribution for known investors, or restore them after archival.

TTL constants (both contracts)

Constant	Value
PERSISTENT_LIFETIME_THRESHOLD	DAY_IN_LEDGERS * 30 (518,400 ledgers, ~30 days)
PERSISTENT_BUMP_AMOUNT	DAY_IN_LEDGERS * 90 (1,555,200 ledgers, ~90 days)

Suggested indexer cadence: call touch_campaign about every 30 days. extend_ttl is a no-op while remaining TTL is still above the 30-day threshold.

If an entry has already archived, restore it with RestoreFootprintOp first; touch_campaign cannot revive archived keys.

Tests

cd contracts
cargo test -p production_escrow --lib   # 81 passed (78 unit + 3 proptest)
cargo test -p registry --lib            # 47 passed

New coverage:

• TTL actually extends after remaining life drops below the threshold
• No stored state change
• Related terminal keys (tranches / harvest / dispute / activity pages) are bumped
• Missing campaign panics with the archival-aware message

Payout wallet: GBVHELLD2JE235Y2NGTDT3MWI3T65ON6SY4N6FBHYVDAQ5FZC2CP5QXH

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