feat(config): add read-only global config view

[Baskarayelu]

Summary

Adds GlobalConfig and get_global_config(), a read-only view aggregating the contract's global (non-pair-scoped) configuration — fee recipient, absolute fee ceiling/floor, oracle, and timelock delay — into a single call instead of five separate getters. Every field returns its existing documented sane default, so the view is safe to call pre-init.

Includes tests for: pre-init defaults, values after configuration, and that the view is side-effect free.

Test output

main currently fails to build at HEAD with ~100 pre-existing, unrelated errors (duplicate top_up_pair_liquidity definitions from a prior merge — confirmed via git stash that this reproduces with zero local changes). This is out of scope for this PR. I verified the new code adds zero additional errors via cargo build --tests 2>&1 | grep -i global_config (no matches) and manually reviewed the new GlobalConfig/get_global_config code against the existing getter patterns it mirrors.

Closes #409