docs(specs): Shakedex selling stage — expiry guard, restore a lock by name, delivery plan

[DimazzzZ]

Spec amendments for the Shakedex selling stage (PR 2), decided before any selling code is written.

What changes

• R31 — No lock that cannot reach the market (new). Lock and Finalize & sign are refused when the name would expire before the seller's own FINALIZE into the lock: expiry_end <= tip + 1 + remaining lockup + 1 day (R9's margin), where the remaining lockup is the full transferLockup at Lock and NameParams::blocks_until_finalize of the lock TRANSFER at Finalize & sign. Below six months from the tip to expiry_end, the Lock dialog warns. Grounded in hsd 8.0.0: FINALIZE renews a name (chain.js, ns.setRenewal(height)), TRANSFER does not, so the only expiry risk is the lockup.
• R32 — Restore a lock by name (new). A restored wallet adopts a lock when the name's current owner coin sits at the lock address derived from the seed and carries FINALIZE at the name's height; it names what it refuses (expired name, a name not at our lock, a name still locking, a lock coin already a TRANSFER, a leftover lock coin). Importing the saved listing file restores the listing details.
• §5 Known gaps: lock recovery is manual in this stage; the automatic address-history scan is deferred to the roadmap. ADR 0004 gets a dated amendment saying so; its decision is unchanged.
• R27: the listing lasts up to renewalWindow after the FINALIZE into the lock, which renews the name.
• R19 / R23 / R25: UI placement (Sell in Owned Names, a "My listings" tab on the Market page), and the daemon contract: never signs or broadcasts, publishes listings already signed to LearnHNS Market (SECURITY.md follows in the publishing PR).
• R1, R4, R16–R30: Enforced/Pinned names aligned with the delivery plan; R29 gets its own lines; backend refusal of out-of-range prices (R19) and schedules (R24), and re-listing after a cancel tracking only the new lock outpoint (R28).
• §6 Delivery: selling ships as a stack of PRs (lock keys and P2WSH signing, seller transactions, lock, finalize and sign, tracking and Sold, cancel and lower price, publishing, UI, reverse auctions, docs).
• CONTEXT.md: terms Locking, Restored lock, My listings.

Checks

• npx prettier --check . passes.
• R31's and R27's renewal claims checked against the hsd 8.0.0 source; test and function names checked against the delivery plan in both directions.
• Docs only; no code or tests change.