fix:master_wallet can't be deleted or duplicated

[mrnkslv]

Summary

Reserve the logical wallet name master_wallet in nodectl: operators cannot config wallet add a regular wallet with that name (it remains the master’s slot in config wallet ls), and config wallet rm fails immediately with a clear error when that name is used—without loading the config or suggesting “not found”. The name is defined once as MASTER_WALLET_RESERVED_NAME in utils.rs and reused by get_wallet_config, WalletAddCmd, WalletLsCmd, and WalletRmCmd so resolution and CLI checks stay aligned.

Changes

• utils.rs
  Add public MASTER_WALLET_RESERVED_NAME ("master_wallet") with a short comment: CLI / get_wallet_config / config wallet ls.
  get_wallet_config: resolve the master wallet when name == MASTER_WALLET_RESERVED_NAME instead of a hardcoded literal.
• config_wallet_cmd.rs
  Import MASTER_WALLET_RESERVED_NAME from utils (no duplicate local constant).
  WalletAddCmd: reject --name equal to MASTER_WALLET_RESERVED_NAME; error text uses the constant (e.g. '{}' is a reserved name).
  WalletLsCmd: append the master row with MASTER_WALLET_RESERVED_NAME.
  WalletRmCmd: before AppConfig::load, if the target equals MASTER_WALLET_RESERVED_NAME, bail with The master wallet cannot be removed (no config mutation).

Closes SMA-48

[linear]

SMA-48 Protect master wallet from conflicts

[Copilot]

Pull request overview

This PR fixes an issue where master_wallet could be deleted or duplicated by reserving it as a special wallet name. The fix centralizes the wallet name string in a constant MASTER_WALLET_RESERVED_NAME and uses it consistently across add, remove, and list operations. The remove operation also adds an early error check to prevent deletion of the master wallet with a clear error message.

Changes:

• Introduce MASTER_WALLET_RESERVED_NAME constant to define the reserved wallet name once
• Update WalletAddCmd to check against the constant instead of a hardcoded string
• Update WalletLsCmd to use the constant for displaying the master wallet
• Add early validation in WalletRmCmd to prevent removal of the master wallet

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[Copilot]

The constant MASTER_WALLET_RESERVED_NAME is defined with the note that it's accepted by get_wallet_config, but the function in utils.rs (line 139) still uses a hardcoded string literal "master_wallet" instead of this constant. For consistency and maintainability as stated in the PR description ("The string is defined once as MASTER_WALLET_RESERVED_NAME and reused for add, rm, and ls so the behavior stays aligned"), this should be updated to use the constant.

[mrnkslv]

done