Fix governance proposal kind ambiguity

[carrion256]

Summary

Fixes governance proposal broad-kind ambiguity and documents the in-flight timelock policy with one finding-scoped commit per fix:

• #FIND-065 — accept_kind ambiguity when multiple pending proposals share the same broad action kind.
• #FIND-088 — revoke_kind previously cancelled all proposals of a broad kind while accept_kind accepted only one.
• #FIND-095 — in-flight proposals intentionally retain the submit-time timelock even if that timelock is raised later.

Commits

• fix governance accept kind ambiguity (#FIND-065)
• fix governance revoke kind semantics (#FIND-088)
• test governance in-flight timelock policy (#FIND-095)

Changes

• Make accept_kind fail with GovernanceError::DuplicatePending when more than one pending proposal matches the requested broad GovernanceActionKind.
• Make revoke_kind use the same exactly-one broad-kind policy instead of revoking every matching proposal.
• Keep proposal-id and action-key revocation paths unchanged for precise proposal management.
• Add regressions for ambiguous CapGroup acceptance, ambiguous TimelockConfig revocation, and submit-time timelock semantics.

Triage notes

• #FIND-091: current branch already carries focused no-change/classifier coverage around duplicate submissions, cap/group classifiers, and membership clear semantics; no additional code change was needed in this PR slice.
• #FIND-059: current branch already mirrors cap-group membership state and tests membership clear/no-change classification.
• #FIND-061: not changed here; broad abdication remains kind-level by design unless product wants a new precise-action abdication API.

Verification

• cargo fmt -p templar-soroban-governance
• cargo test -p templar-soroban-governance accept_kind_rejects_ambiguous_broad_kind -- --nocapture
• cargo test -p templar-soroban-governance revoke_kind_rejects_ambiguous_broad_kind -- --nocapture
• cargo test -p templar-soroban-governance in_flight_proposal_keeps_submit_time_timelock_after_timelock_raise -- --nocapture
• cargo test -p templar-soroban-governance -- --nocapture
• post-commit hook: Soroban size-budget-check passed (93961 bytes)

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