[team feature] Team proposal and vote for chunk claims

[tastybento]

Split out of #6, which asked for five ways of deciding who may claim a chunk. Three of them shipped in 1.1.0 as the CHUNKBLOCK_CLAIM_CHUNKS island flag (owner only / sub-owner and up / any configurable rank), and #6 is closed for those. The remaining two are a different kind of thing and are tracked here.

Original request from @mrfloris in #6:

chunks can be claimed by?

• Owner only
• Sub-owner or higher
• Configurable island rank
• Team proposal requiring owner approval
• Team vote

Why these are not just another rank

The shipped flag answers "does this player have the authority to spend credit, yes or no" — a single check at the moment of the click. A proposal or a vote is a workflow with state that outlives the click:

• a pending proposal has to be persisted on the island (which chunk, who proposed it, when), and survive restarts
• it needs an expiry, or islands accumulate stale proposals forever
• somebody has to see it: a pending-claims list, a prompt on login for the approver, or a marker on /ch chunks
• the level credit has to be re-checked at approval time, not proposal time — the island may have lost levels in between, and the chunk may have become unclaimable (re-locked neighbour, protection range)
• a vote needs a quorum rule, a tiebreak (owner breaks ties, per [team feature] Branching phase paths with team voting #5), and a policy for members who never respond

Relationship to #5

#5 (branching phase paths with team voting) needs the same machinery: a proposal, a quorum, an expiry, a tiebreak, and a UI to cast a vote. If both get built, the voting mechanic should be written once and consumed by both, rather than a claim-vote and a phase-vote growing separately. Whichever is built first should carry the generic part.

Notes on scope

• The wasted-credit worry that motivated Team chunk-claim governance #6 is already handled for everyone by the claim confirmation added in Confirm chunk claims before spending level credit #17 — the first hit previews and quotes the price, and only a sneaking second hit spends anything. So this is no longer about preventing accidents; it is about giving a team a say. Worth keeping in mind, because it lowers how much this needs to do.
• Proposal-with-owner-approval is much the cheaper half: no quorum, no tiebreak, one approver. It could ship alone and would cover most teams.
• A pending proposal drawn on the territory map would fold in nicely with the map marker follow-up mentioned at the end of Team chunk-claim governance #6.