Fix market payout and configuration safety

[Ayg001]

Summary

• [LOW][fees] DEFAULT_TIMELOCK_SECONDS is 86400 (24h) but there is no minimum timelock enforcement #255 Fees timelock: Route set_platform_fee through the queued update flow and enforce the 1-hour minimum delay while retaining the 24-hour default.
• [LOW][admin] set_admin_cooldown allows setting cooldown to 0 — effectively disabling cooldowns #256 Admin cooldown: Reject cooldowns below 60 seconds; add an authorized disable_admin_cooldown entrypoint for explicit opt-out.
• [HIGH][markets] MarketCounter overflow: no upper bound on number of markets #259 Market cap: Add an admin-configurable market limit with a finite 10,000-market default and reject creation at the cap.
• [HIGH][markets] Payout calculation uses integer division — precision loss causes fund leakage #260 Payout rounding: Carry proportional division remainders between claims per outcome and allocate pool-split remainder deterministically; document the policy.

Validation

• Editor diagnostics and CRLF-aware git diff --check passed.
• Cargo tests could not run because Cargo is unavailable in the environment.

Fixes #255
Fixes #256
Fixes #259
Fixes #260

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