feat!: rename LGT to AVOW + pin chain v0.3.0 (DO NOT MERGE until chain deploys)

[proofmancer]

⚠️ DRAFT — do not merge until chain v0.3.0 deploys to the public devnet that replaces ligate-devnet-1. This CLI binary is incompatible with the still-LGT devnet-1; merging early ships a broken ligate to anyone tracking main.

Cross-repo follow-up to ligate-chain#457. Closes #39.

Summary

• $LGT → AVOW everywhere. Per the cleaner convention adopted chain-side, the leading $ drops from the prose ticker. Substitutions cover display strings, doc comments, README, CHANGELOG, and internal Rust identifiers.
• Chain dep pin: branch = "main" → tag = "v0.3.0" for ligate-client, ligate-stf, ligate-rollup. Explicit version coupling.
• SDK pin bumped to chain v0.3.0's canonical revs: Sovereign-Labs/sovereign-sdk@f6cd64749ed... and ligate-io/sovereign-sdk@ffff9dfe6b6... (was f89964c66bc... and eab3f9d0ae0...).
• Wire-field renames in faucet + balance: drip_amount_lgt → drip_amount_avow, amount_lgt → amount_avow. Aligned with ligate-api#70's wire-shape flip.

Coordination

Holds for the same cutover window as ligate-api#70. Order:

1. Chain v0.3.0 deploys to ligate-devnet-2
2. ligate-api#70 merges + Railway redeploys api against the new chain
3. Mark this PR ready + merge. Release workflow builds + publishes v0.3.0 of the CLI; operators brew upgrade or re-download
4. Until (3), ligate-cli v0.2.1 keeps working against devnet-1

Test plan

• CI green (cargo fmt / clippy / check / test)
• No Llgt`` matches anywhere after substitution (verified locally; rg returns empty)
• After chain deploy + api flip: ligate balance lig1… prints AVOW (manual smoke)

[proofmancer]

I have read the CLA Document and I hereby sign the CLA