Add AutoCompoundFacet for keeper-driven compounding

[vonMangoldt]

Publishes the keeper-driven auto-compound facet that is deployed and source-verified on all four chains, with its selector proposals queued on all nine vaults, so the public repo matches the upcoming selector surface.

What is included

• AutoCompoundFacet with compoundInterestOnBehalf(user): a master-allowlisted keeper bot compounds an opted-in user's settled interest into vault shares and keeps autoCompoundFeeBps (target 100 = 1%, hard cap 500) of the interest as its USD reward. The compound is the audited compoundInterest flow plus a fee split: identical modifier order, interest bucket cleared and net shares minted before the two USD transfers, and fee + net exactly offsets the cleared liability, so the accumulator identity and the sweep-buffer reservation hold. Both gates are required (master allowlists the bot, the user opts themself in), a bot compound stamps the grace lock on the minted net, and opting out is always callable, even while the vault is paused.
• AutoCompoundDeclaration storage tail shard (slots 64-66: isAutoCompoundBot, autoCompoundAllowed, autoCompoundFeeBps), appended last in the declarations chain. This is the first shard activated onto the already-live diamonds: safe because the deployed layout ends at slot 63, so no live code path reads or writes the new slots.
• Seven routed selectors per vault: the four functions plus the shard's three compiler-generated getters, which the frozen live dispatchers cannot serve natively.
• The CompoundInterestOnBehalf, AutoCompoundBotSet, AutoCompoundAllowedSet and AutoCompoundFeeBpsSet events, the three errors, the autoCompoundSelectors() library entry with its getter mirror interface, the full-identity FACETS entry in check_storage_layout.sh, the regenerated layout snapshot plus the STORAGE_LAYOUT.md section, script/check_live_layout_prefix.sh (anchors the snapshot to the deployed code by compiling the verified source and byte-comparing the on-chain runtime), and the unit suite.

Live deployments (proposals queued on all nine vaults)

Chain	AutoCompoundFacet
Ethereum	0xb1413B9f72e856f2aA7a91d68e6bdF00A0149b60
Base	0x80f9398b4d9F4a0Fa9A108716c902C2B56BD535A
Arbitrum	0xc40c93A30B18d5dCc0E4C59f33f7369E4472c521
Robinhood	0x0f63bDcE0f4f3531117E2ed2FE1484c5E40a75b5

All four instances are source-verified on their explorers. Selectors: 0x7d31de9c compoundInterestOnBehalf, 0x430187af setAutoCompoundAllowed, 0x42c71bd2 setAutoCompoundBot, 0x6656b5a8 setAutoCompoundFeeBps, 0x69102b0b isAutoCompoundBot, 0x5f3743df autoCompoundAllowed, 0x2ba662d6 autoCompoundFeeBps. The timelocked proposals mature on 2026-08-31; execution and fee/bot configuration follow then.

Verification on this branch

• forge build clean
• New suite: 26 tests, 0 failures, 100% coverage on the facet (lines, statements, branches, functions)
• Full offline suite: 1061 tests, 0 failures
• script/check_storage_layout.sh: diamond + 18 facets identical, 3 slim facets pinned correctly, snapshot matches (74 entries)
• script/check_live_layout_prefix.sh: the deployed diamonds run identical bytecode on all nine vaults, their layout is an exact prefix of the committed snapshot, and slots 64-66 are untouched zeros for every live code path