Add CLI transaction cost confirmations

[AgentGoose32]

What does this pull request do? Explain your changes. (required)

Adds a transaction confirmation step to livepeer_cli that shows an estimated maximum ETH cost before common wallet-affecting transaction actions are submitted to the local node.

Specific updates (required)

• Adds confirmTransaction() and httpPostTxWithParams() helpers in the CLI wizard.
• Shows an estimated maximum transaction cost using the configured max gas price and a standard 21,000 gas baseline when max gas price is available.
• Falls back to an explicit "unavailable" estimate message when max gas price is unset.
• Requires explicit y/n confirmation before submitting bond, rebond, unbond, withdraw stake/fees, transfer LPT, and fund deposit/reserve calls.

How did you test each of these updates (required)

• Ran gofmt on changed files.
• Ran git diff --check successfully.
• Installed Go, pkgconf, and ffmpeg locally and attempted go test ./cmd/livepeer_cli. The package build reaches existing upstream github.com/livepeer/lpms/ffmpeg C bindings, but fails against Homebrew ffmpeg 8.1 with undeclared avfilter_compare_sign_* symbols. This appears to be a local ffmpeg/LPMS compatibility issue rather than a syntax error in this CLI patch.

Does this pull request close any open issues?

Fixes #1815

/claim #1815

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated