Add artisan commands for feature flag management

[stevethomas]

Summary

Re-opened from #5. Originally merged but reverted from main to keep v1.x clean — this is targeted at v2.

• feature:manage — interactive table to toggle feature states
• feature:on / feature:off — turn individual features on/off
• feature:set — set a feature to a specific state (on/off/dynamic)

Test plan

• Existing tests pass
• New command tests pass
• Commands work interactively via php artisan

[sentry]

Bug: The ManageFeaturesCommand does not handle a potential MissingFeatureException, which can cause the artisan command to crash if a feature is not found during execution.
_{Severity: LOW}

Suggested Fix

Wrap the call to FeatureFlag::updateFeatureState() at line 47 of ManageFeaturesCommand.php within a try-catch block. Catch the MissingFeatureException and output a user-friendly error message to the console, consistent with the error handling in other feature flag commands.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: src/Commands/ManageFeaturesCommand.php#L47

Potential issue: The `ManageFeaturesCommand` calls `FeatureFlag::updateFeatureState()`
without a `try-catch` block. If a feature is not found, `updateFeatureState()`
internally calls `getFeatureModel()`, which throws a `MissingFeatureException` by
default. This can occur in a race condition where a feature is deleted from the database
after the command has loaded the list of features but before the user selects one to
manage. Unlike other commands like `TurnOnFeatureCommand` which handle this exception,
`ManageFeaturesCommand` will crash with an unhandled exception instead of displaying a
graceful error message to the user running the command.

_{Did we get this right? 👍 / 👎 to inform future reviews.}