Add SuperTokenV1Library notes and update docs

[youngkidwarrior]

Why:
Record library usage patterns and refine project planning
documents for clarity.

Test plan:

• Open SuperTokenV1Library.md and PLAN.md.

[youngkidwarrior]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• Add SuperTokenV1Library notes and update docs #21 👈 (View in Graphite)
• Update Ignition module and params to use SENDx #20 : 1 other dependent PR (#22 )
• Test passing SENDx to RewardsManager #18 : 1 other dependent PR (#19 )
• Accept existing SuperToken in RewardsManager ctor #15 : 1 other dependent PR (#16 )
• Add RewardsManager for pool units sync #13 : 1 other dependent PR (#14 )
• Update wrapper cache for anvil (845337) #23 : 1 other dependent PR (#33 )
• Add UNDERLYING_ADDRESS override for wrapper #17
• Wire anvil-deploy to wrapper script; set signer #9 : 1 other dependent PR (#10 )
• Test wrapper metadata and upgrade/downgrade #8
• Align viem calls and env discovery in tests #26 : 1 other dependent PR (#27 )
• Ensure hardfork=cancun on hardhat network #25
• Add test/type dependencies and refresh bun.lock #24
• Add CFAv1Forwarder field (optional) #12
• Add Superfluid config and deployments scaffold #6 : 1 other dependent PR (#7 )
• Remove legacy lockbox code; rename Tilt resource #5
• Rename package name #3 : 1 other dependent PR (#4 )
• Scaffold project from send-token-upgrade #2
• Initialize README for SuperToken wrapper #1
• main

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