spec: fill in missing pages

[TalDerei]

Currently, we lack complete documentation of the protocol, and stub the following pages in the protocol spec:

• [Key Agreement] - (./crypto/decaf377-ka.md)
• [The eddy construction] - (./crypto/flow/eddy.md)
• [LPNFTs] - (./dex/lpnft.md)
• [Position Actions] - (./dex/action/position.md)
• [Delegate] - (./stake/action/delegate.md)
• [Undelegate] - (./stake/action/undelegate.md)
• [ValidatorVote] - (./governance/action/validator_vote.md)
• [Proposal Actions] - (./governance/action/proposal.md)
• [CommunityPoolSpend] - (./community_pool/action/spend.md)
• [CommunityPoolOutput] - (./community_pool/action/output.md)
• [CommunityPoolDeposit] - (./community_pool/action/deposit.md)