feat(registry): name expiry with renewal payments and grace re-registration #2

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Description

Names are registered forever once claimed — combined with free registration this means the namespace can be fully squatted. DNS/ENS convention is annual renewal: names expire unless renewed, and expired names become registrable again. Soroban's persistent-storage TTL already gives us the machinery; this issue adds the economic layer on top.

Desired outcome: each name carries an expires_at ledger timestamp; renew(name) extends it for a fee; a new reclaim(name) entrypoint lets anyone re-register a name whose expiry passed, deleting the stale record first.

Scope

• Crate/module: crates/registry, src/lib.rs
• API: renew(name), reclaim(name), read-only expiry_of(name) -> u64; Resolution gains expires_at
• Storage: DataKey::Expiry(String) (persistent, TTL-extended alongside the name key)
• Tests: renew extends by exactly one year-equivalent; renew on unregistered name → NotFound; reclaim before expiry → InvalidInput; reclaim after expiry resets owner/address/counter; TTL interplay between expiry key and name key
• Docs: renewal/expiry section in docs/ and README

Non-goals

• Auto-renewal subscriptions (needs pull-debit — out of scope)
• Grace periods with premium pricing (single flat re-registration price)
• Refunds on early reclaim
• Pricing changes (the pricing issue owns fee levels; this uses a constant renewal price or integrates price_for if it has landed)

What "done" looks like

• register sets expires_at = now + REGISTRATION_PERIOD (documented constant, ~1 year in ledgers)
• resolve returns expires_at; UI-consumable
• renew requires owner auth (or anyone, if paying — pick one, document, test) and extends expiry
• reclaim deletes + re-creates the record when now > expires_at, otherwise errors
• New error variants use the next free codes; enum test updated
• All existing 15 tests stay green; new tests cover every branch above
• fmt/clippy/tests/WASM-build gates pass

Implementation guidelines

• The name and owner keys already extend TTL on write/hot-read (extend_ttl in register/resolve) — the expiry key must join those bumps or it will archive before the name
• Compare set_address/transfer for the owner-check pattern (require_owner helper exists)
• reclaim should reuse register's validation path for the new owner
• Consider whether resolve should fail with a new Expired error when past expiry — design note: prefer returning the record + expires_at and letting reclaim gate re-registration, but state your choice in the PR
• Constants belong at module top with the existing TTL constants

Verification

cargo fmt --all -- --check
cargo clippy --workspace --all-targets --locked -- -D warnings
cargo test -p sidera-registry --all-targets --locked

PR guidelines

• Get assigned before starting; do not start work on a reserved issue.
• Work in a fork; branch off upstream/main; open the PR against Sidera-Protocol/sidera-contracts:main.
• PR description must include Closes #2.
• State before/after storage behavior explicitly (which keys changed).
• All CI checks must pass; human maintainer review required.

Metadata

• Affected crates/files: contracts/registry/src/lib.rs, docs/
• Complexity label: complexity: medium (150 base points)
• Type labels: enhancement