docs: add contributing guide and trim CLAUDE.md

[dev-jodee]

Summary

• Add CONTRIBUTING.md: before-you-start rules, signed commits, security reporting, development setup, change checklist, PR expectations, and an AI-use section (review expectations, disclosure, code smells, communication)
• Fill it with repo specifics: just recipes, regenerating IDL/clients and the check-generated CI gate, Pinocchio (no anchor-lang), ADRs, CU report, CODEOWNERS review
• Trim CLAUDE.md from 120 to 55 lines: keep only non-obvious repo gotchas (non-Anchor wire format, IDL as a build-script side effect, raw-bytes versioning, two-pass TypeScript tests, LiteSVM clock, no BigInt toJSON patch), drop everything derivable from the repo itself

Test Plan

• Docs only, no code paths touched
• Commands referenced verified against justfile (setup, check, test, generate-clients, check-generated, test-and-benchmark) and workflows (idl-check.yml, benchmark.yml)

[vercel]

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Project	Deployment	Actions	Updated (UTC)
solana-subscriptions-program	Ready	Preview	Aug 27, 2026 12:42pm

[github-actions]

Compute Unit Report

Instruction	Samples	CUs	Est Cost (Low) [SOL]	Est Cost (Med) [SOL]	Est Cost (High) [SOL]	Δ Avg vs main
cancel_subscription	28	1838	0.000005000	0.000005073	0.000005919
cancel_subscription_now	5	1873	0.000005000	0.000005074	0.000005936
close_subscription_authority	22	1804	0.000005000	0.000005072	0.000005902
create_fixed_delegation	50	3524	0.000005001	0.000005140	0.000006762
create_plan	141	3501	0.000005001	0.000005140	0.000006750
create_recurring_delegation	35	3561	0.000005001	0.000005142	0.000006780
delete_plan	10	359	0.000005000	0.000005014	0.000005179
init_subscription_authority	231	6310	0.000005001	0.000005252	0.000008155
resume_subscription	4	2041	0.000005000	0.000005081	0.000006020
revoke_abandoned_delegation	3	403	0.000005000	0.000005016	0.000005201
revoke_abandoned_subscription	2	2093	0.000005000	0.000005083	0.000006046
revoke_delegation	24	282	0.000005000	0.000005011	0.000005141
revoke_subscription_authority	8	3570	0.000005001	0.000005142	0.000006785
subscribe	52	6642	0.000005001	0.000005265	0.000008321
transfer_fixed	10	5641	0.000005001	0.000005225	0.000007820
transfer_recurring	21	5749	0.000005001	0.000005229	0.000007874
transfer_subscription	14	6029	0.000005001	0.000005241	0.000008014
update_plan	31	2142	0.000005000	0.000005085	0.000006071

🔺 increase · 🔻 decrease · – unchanged · 🆕 new · 🗑 removed (vs main)

Generated: 2026-08-27