Use 'token' instead of 'instrument' in UI and CLI for consistency

[zheli]

Problem

The token management screen in the Web UI uses the term instrument in several places (labels, headings, form fields) while the rest of the UI — and the product itself — refers to the concept as a token. This inconsistency is confusing to users who encounter the word "instrument" without context.

The CLI has the same issue: --instrument flags appear on token subcommands where a user would expect --token.

Proposed changes

Web UI

• Replace all instances of "instrument" in user-facing copy on the token screen with "token".
• Add a brief contextual note on the token screen explaining the relationship between token and instrument (a token is the balance held by a party; an instrument defines the asset type, unit, and issuer that backs it). Link to the Canton / Daml Finance documentation for users who want the full definition.

CLI

• Rename --instrument to --token as the primary flag name on all token subcommands.
• Keep --instrument as a deprecated alias so existing scripts do not break.
• Add a short note to the flag usage string (and/or the command Long description) explaining that "instrument" is the underlying Daml Finance term for the asset type that a token is denominated in, with a link to the official Daml Finance docs: https://docs.daml.com/daml-finance/reference/instrument-overview.html

Acceptance criteria

• Web UI token screen uses "token" everywhere in user-facing labels, headings, and button text.
• A contextual note on the Web UI token screen explains token vs. instrument and links to Daml Finance docs.
• CLI --instrument flag is renamed to --token; --instrument remains as an alias.
• CLI --token / --instrument flag description includes a brief token-vs-instrument explanation and a link.
• All changes pass make test and make lint.
• CLI and Web UI changes land together (CLI ↔ Web UI parity rule).