feat(webapp): add custom RPC option to network menu

[dev-jodee]

Summary

• Add a Custom RPC entry to the top-right network selector (explorer.solana.com–style) so users can point the app at their own Solana RPC URL.
• Single saved slot in localStorage; gets its own solana:custom cluster + network config (config/networks.ts).
• Provider includes the saved custom cluster on init and accepts the solana:custom id; clusterIdToNetwork resolves it to a new custom network.
• Dropdown gains Add/Edit custom RPC (URL dialog with validation) and Remove custom RPC.

Test Plan

• Run the webapp (pnpm --filter @solana/subscriptions build first, then cd webapp && pnpm dev).
• Top-right Network menu → Add custom RPC → paste an RPC URL → Save. Page reloads, selector shows Custom, app uses that endpoint.
• Invalid URL → toast error, no save.
• Reopen menu → Edit custom RPC (prefilled) / Remove custom RPC (clears + reverts to default).

Notes / assumptions

• Custom maps to mainnet token/program config by default (program id is identical across clusters; default token = mainnet USDC). Pointing at a local/forked validator means the mainnet USDC mint won't exist there — mints can be entered manually.
• Faucet/some nav hidden on custom (clusterFilter matches exact ids) — expected.
• Verified: tsc -b + eslint clean. Not runtime-verified (needs live RPC + wallet).

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Project	Deployment	Actions	Updated (UTC)
solana-subscriptions-program	Ready	Preview, Comment	May 29, 2026 5:01pm

[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	22	1720	2030	1919	0.000005000	0.000005076	0.000005959
close_subscription_authority	10	1803	1833	1806	0.000005000	0.000005072	0.000005903
create_fixed_delegation	41	3517	20022	5119	0.000005001	0.000005204	0.000007559
create_plan	97	3436	12436	4877	0.000005001	0.000005195	0.000007438
create_recurring_delegation	29	3550	11055	4849	0.000005001	0.000005193	0.000007424
delete_plan	9	359	359	359	0.000005000	0.000005014	0.000005179
init_subscription_authority	173	6226	21226	9517	0.000005002	0.000005380	0.000009758
resume_subscription	3	1723	1723	1723	0.000005000	0.000005068	0.000005861
revoke_delegation	19	255	519	353	0.000005000	0.000005014	0.000005176
subscribe	32	6485	12485	7335	0.000005002	0.000005293	0.000008667
transfer_fixed	9	5479	9966	7364	0.000005002	0.000005294	0.000008682
transfer_recurring	19	5591	10091	7071	0.000005002	0.000005282	0.000008535
transfer_subscription	10	5838	10340	7343	0.000005002	0.000005293	0.000008671
update_plan	22	424	503	477	0.000005000	0.000005019	0.000005238

Generated: 2026-05-29