Closes #7652

Problem

Opening /project/<p>/environment/<e>/features?feature=<id>&tab=<tab> did not open the feature slideout when the targeted feature was not on the currently rendered page of the paginated list. Deep-linking was handled per-row inside FeatureRow, so if no row mounted for the feature (e.g. it sorts past page_size=50), the effect never fired and the slideout never opened. The failure was silent, with nothing reaching Sentry.

Fix

Detect, at the page level, when the ?feature= target is missing from the loaded page and fetch it directly, then render a hidden FeatureRow so the existing deep-link effect opens the slideout (honouring the tab param).

• shouldDeepFetchFeature decides whether a direct fetch is needed (no-ops when there is no param, the list has not loaded, the param is not a valid id, or the feature is already on the page).
• useDeepLinkedFeature fetches the project flag and its environment feature state when required.
• FeaturesPage renders a hidden row for the fetched feature; the on-page path is unchanged, so there is no double-open.

Behavior is now independent of pagination, sort order, and tag/archive filters.

Testing

• Unit tests for shouldDeepFetchFeature and pickEnvironmentFlag (8 cases) — passing.
• E2E test covering a deep link to an off-page feature.
• Typecheck: the changed files introduce no new type errors.