chore: rename LGT to AVOW across CLI commands + README (tracks ligate-chain#457)

[proofmancer]

What

Update LGT / ulgt references to AVOW / uavow across the operator + builder CLI.

Tracks: ligate-io/ligate-chain#457 (umbrella)

Why

Token symbol rename: $LGT → $AVOW. CLI must speak the new denom or ligate balance, ligate transfer, ligate faucet all break against the new devnet. Full rationale in the umbrella issue.

Files to change

Found via rg '\$LGT|"LGT"|ulgt|ligate gas token':

• constants.toml
• src/cli.rs
• src/transfer.rs
• src/balance.rs
• src/attest.rs
• src/faucet.rs
• README.md
• CHANGELOG.md

Concrete substitutions

Find	Replace with
ulgt	uavow
LGT (display in CLI output)	AVOW
$LGT (README prose)	$AVOW
"Transfer $LGT" / "Drip $LGT" copy	"Transfer $AVOW" / "Drip $AVOW"

Timing

Must release a new CLI version before ligate-devnet-2 launches. The CLI README is the first thing new operators read; if it says $LGT while the chain says uavow, the first user experience is broken.

Suggested versioning: bump to v0.3.0 (breaking output format, denom changed). Per the versioning convention (clean-semver, no -devnet suffix), plain v0.3.0.

Done when

• Zero ulgt / LGT matches in rg
• ligate balance shows AVOW
• ligate transfer --denom uavow works against a local node with the new denom
• Brew tap + binary releases for the new version published