docs(natspec): apply house documentation standard across all contracts

[jayeshy14]

Extends the NatSpec + section-banner standard you started by hand in CPPIVault.sol to the entire codebase.

What changed

• Boxed section banners on every file, replacing the old // ---- x ---- dividers.
• Per-member NatSpec on every state var, constant, struct (+ @param per field), event (+ @param per param), and error.
• Full function NatSpec — @notice + @param for every argument + @return for every return value — on every external/public/internal function across all 15 source files.
• IOracleHealth extracted into src/interfaces/IOracleHealth.sol (fixing the IOracleHeath filename typo) and imported into CPPIVault.
• Trailing inline comments promoted to NatSpec above their declaration.

Preserved deliberately

• Every audit reference and rationale kept verbatim in meaning (H1/H2, H3, H5, H6, M1, M2, M3, M4, L1–L8, I1–I3, G2 guard).
• No code, signatures, logic, or ordering changed.

Two benign, intentional deviations from "comments only"

1. The IOracleHealth interface extraction/rename (you initiated this).
2. Named previously-unnamed interface return values (e.g. returns (uint256) → returns (uint256 valueWad)) so @return tags bind. Return names are not part of the ABI, so this is semantically inert.

Verification

• forge build clean.
• 151 / 151 tests pass (proves no behavior changed).
• A declaration scan reports 0 undocumented functions/events/errors/structs across src/.
• A diff filter confirms the only non-comment code deltas are the two deviations above.

Docs only.