docs: remove stale --osx-sign.entitlements CLI options from usage.txt

[claude]

Requested by Samuel Attard · Slack thread

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable). (N/A — help-text-only change)
• The testsuite passes successfully on my local machine (if applicable). (yarn lint passes; no code changes)

Summarize your changes:

Before: --help (via usage.txt) promised that --osx-sign.entitlements and --osx-sign.entitlements-inherit could be used to set signing entitlements from the CLI. In reality, since @electron/osx-sign >= 1.0 these flags are silently ignored and the default entitlements are used instead: per-file signing options such as entitlements can only be supplied through an optionsForFile function on the sign options, which the CLI's dot-notation cannot express (and entitlements-inherit no longer exists as an option at all).

After: the help text no longer advertises the non-functional flags. It keeps the working identity example and adds a note that per-file signing options such as custom entitlements cannot be set from the CLI, pointing users to the JavaScript API's osxSign.optionsForFile function and the @electron/osx-sign docs.

No other docs make the same stale claim (README, docs/, and JSDoc were checked); the binaries JSDoc inaccuracy in src/types.ts is tracked separately in #1723.

Fixes #1854

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https://claude.ai/code/session_01Gjy8Kvb56YvEgBhhGEqeNF

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