fix: include rust client readme in crate

[dev-jodee]

Summary

• Point the Rust client crate at the repo-root README, matching Kora's crate metadata pattern.
• Include the repo-root README in the crate package allowlist while keeping generated Rust sources included despite generated/ being gitignored.
• Bump the Rust client crate to 0.1.2 so the README can appear on crates.io in the next immutable release.

Test Plan

• cargo check -p subscriptions --locked
• cargo package --list --allow-dirty
• cargo publish --dry-run --locked --allow-dirty
• git diff --check
• pre-push hook: format check and lint check

[github-actions]

Compute Unit Report

Instruction	Samples	Min CUs	Max CUs	Avg CUs	Est Cost (Low) [SOL]	Est Cost (Med) [SOL]	Est Cost (High) [SOL]
cancel_subscription	11	1805	2118	2003	0.000005000	0.000005080	0.000006001
close_subscription_authority	7	1881	1916	1886	0.000005000	0.000005075	0.000005943
create_fixed_delegation	38	3621	11147	5347	0.000005001	0.000005213	0.000007673
create_plan	84	3540	11040	5168	0.000005001	0.000005206	0.000007584
create_recurring_delegation	27	3640	12645	5813	0.000005001	0.000005232	0.000007906
delete_plan	8	416	416	416	0.000005000	0.000005016	0.000005208
init_subscription_authority	142	7849	22851	12300	0.000005003	0.000005492	0.000011150
revoke_delegation	19	318	585	420	0.000005000	0.000005016	0.000005210
subscribe	21	6666	11190	7676	0.000005002	0.000005307	0.000008838
transfer_fixed	6	10105	14602	11104	0.000005003	0.000005444	0.000010552
transfer_recurring	17	10212	16300	11037	0.000005003	0.000005441	0.000010518
transfer_subscription	10	10495	14946	12000	0.000005003	0.000005480	0.000011000
update_plan	21	424	500	474	0.000005000	0.000005018	0.000005237

Generated: 2026-05-15