fix: harden voting and oracle key validation

[chukwuebuka19]

Summary

• Reject a governance vote when the combined time-weighted and delegated vote weight is zero, before locking the voter's tokens.
• Enforce the documented 3–9 character alphanumeric format for policy oracle keys.
• The requested oracle registration check ([security] OracleVerifier does not validate oracle is registered for data_type #578) and claim submission time bounds ([bug] ClaimsProcessor does not validate claim submission timestamp #579) are already present on main; I verified the plaintext, encrypted, and batch oracle submission paths, and the claim coverage window check.

This PR groups the four assigned validation issues as requested. The code changes address the remaining gaps in #577 and #580.

Closes #577
Closes #578
Closes #579
Closes #580

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