Task 2: Gate `generatedSnapshotDescription` and `assistantInlineCompletions` registration behind assistant config

[cstns]

Description

Both generatedSnapshotDescription and assistantInlineCompletions are currently registered as hardcoded true for all enterprise installations (forge/ee/lib/index.js:42,45), regardless of whether the assistant service is actually configured. This means the features appear available in the UI but fail at
runtime if the assistant service is not set up.

Changes:

• In forge/ee/lib/index.js, change the registration of both flags to check that assistant.enabled is true and assistant.service.url is present before registering as true
• If assistant configuration is missing or disabled, both flags should be registered as false
• This aligns their behaviour with how expertAssistant is already handled (config-driven rather than hardcoded)

Affected lines:

• forge/ee/lib/index.js:42: app.config.features.register('generatedSnapshotDescription', true, true)
• forge/ee/lib/index.js:45: app.config.features.register('assistantInlineCompletions', true, true)

Expected result:

• On enterprise installations with assistant properly configured: both flags registered as true (no change in behaviour)
• On enterprise installations without assistant configured: both flags registered as false, features hidden from UI

Epic/Story

No response

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