Add RBF fee bumping for unconfirmed sends

- Signal opt-in RBF (BIP125, sequence 0xfffffffd) on all new sends so
  they're replaceable.
- "Bump fee" on an unconfirmed sent tx (its detail view): rebuilds the
  same inputs + recipient outputs at the Priority rate, taking the extra
  fee from the change output (pulling in a confirmed coin if change can't
  cover it), re-signs, and routes to a "Replace with a higher fee?"
  confirmation showing old → new fee before broadcasting.
- New keys translated into all 19 locales.

Honest scope: P2A/TRUC/package-relay are L2/pre-signed-tx + node-relay
features that don't apply to a single-sig wallet broadcasting single txs
via public explorers, so they're intentionally out. CPFP (for receives /
unbumpable sends) is a possible follow-up.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

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