Add stablecoin redemption controller quote API

[3esmit]

Goal

Expose a read-only quote for the next redemption-rate controller tick, using
the pure controller and clamp constants introduced by #312.

Scope

• Add a pure stablecoin_ffi quote operation backed directly by
  run_controller_tick, INTEGRAL_CLAMP, and RATE_DELTA_CLAMP.
• Add redemptionRateUpdateQuote() to StablecoinModuleImpl.
• Read and validate protocol parameters, redemption-price state, the configured
  market-price oracle, and canonical clock.
• Project the current redemption price before running the tick, matching the
  on-chain update_redemption_rate order.
• Return canSubmit, machine-readable blockers, current redemption price,
  market price, elapsed milliseconds, next redemption rate, next integral
  term, and clamp metadata. Preserve all fixed-point and signed values as exact
  decimal strings.
• Treat a not-yet-due interval, stale oracle, or zero oracle price as a
  non-submittable quote, not as a fabricated controller output.
• Keep this operation read-only. Transaction submission belongs to the feat(stablecoin): add permissionless pokes for the global state #317
  poke API sub-issue.

Acceptance criteria

• Quote results match run_controller_tick for positive, zero, and negative
  error; proportional-only and PI modes; integral carry-over; both integral
  clamp directions; both rate clamp directions; and worst-case bounded inputs.
• Sign convention matches the program: error = redemption - market, with no
  extra negation before adding the rate adjustment to fixed-point one.
• Oracle ID, freshness, non-zero price, and minimum-update-interval gates match
  the host instruction.
• No floating-point math exists in the FFI or C++ transport layer.
• nix build .#stablecoin-module and relevant Rust/module tests pass.

Dependencies

Depends on the scaffold, redemption-price-state, and current-global-projections
sub-issues under #321.