fix: clarify claim reward payment status

[Siesta0217]

Summary

• Derive the public claim status from sponsor payment progress instead of showing only the claim approval state.
• Show approved/unpaid claims as "Awaiting sponsor reward" and fully paid claims as "Rewarded".
• Add copy clarifying that approved claims waiting on sponsor reward require no contributor-side action.
• Add LiveView coverage for pending and paid claim reward states.

Test Plan

• Added regression tests in test/algora_web/live/claim_live_test.exs
• mix test test/algora_web/live/claim_live_test.exs (not run locally: this environment does not have Elixir/Mix installed; command fails with mix: command not found)

Closes #262

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