feat(vault): deposit flow with auth, token transfer, pause

[Escelit]

feat(vault): deposit flow with auth, token transfer, pause

Closes #224

Changes

Hardened deposit guard ordering: pause → require_auth → amount positivity → authorization → min_deposit → transfer → persist → emit
Fixed event schema: removed caller from topics to match EVENT_SCHEMA.md (topic 0 = Symbol("deposit") only)
Cleaned up stray AllowedDepositors write in set_allowed_depositor
Removed duplicate get_max_deduct definition that blocked compilation
Tests — 155 passing

Unit: owner deposit, allowed depositor deposit, unauthorized rejection, below-minimum, at-minimum boundary, paused vault, balance unchanged on failure, event schema alignment
Property: balance round-trip invariant (100 iterations), unauthorized rejection (100), non-positive amount rejection (100), idempotent depositor management (100)
Security notes

Pause check fires before require_auth — prevents leaking which addresses are authorized during an incident
Transfer-before-persist ensures no internal state mutates if the on-ledger USDC transfer fails
Checked arithmetic on balance update with explicit "balance overflow" panic

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