feat(storage): Admin UI for GCS JSON credentials and File.uri

[ChrisPdgn]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the master branch
• Targets ui-rewrite (current Admin rewrite base)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx, where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Why

Admin UI counterpart to backend Conduit #1509 (feat(storage): add GCS parity and public file URI semantics).

Mapping to Conduit #1509

Backend	Admin UI
google.serviceAccountKeyJson — inline service account JSON	New Google settings field (password input). Path field kept.
ADC when both path and JSON are empty	Both Zod fields optional / empty-string; helper copy documents ADC.
File.uri — stable Conduit-relative path (/storage/getFileUrl/:id)	File details sheet shows Conduit URI with copy-to-clipboard.
File.url / sourceUrl — direct provider/CDN URLs only when container and file are public	Typed as optional on ConduitFile. Actionable download/open/preview still uses getFileUrl(fileId), not file.url.

Leave both Google credential fields empty to use Application Default Credentials. Do not set JSON if a key path is provided.

Zod note: fields use .optional().or(z.literal('')).default('') so an omitted backend serviceAccountKeyJson becomes '' and stays assignable to StorageSettings on save (no change to settings.tsx).

Test plan

• Storage settings → provider Google: path field still present; JSON field appears with helper text.
• Save with both credentials empty (ADC). Form validates.
• Save with only path, or only JSON. Form validates.
• Switching away from Google shows the cog if either path or JSON is set.
• Settings still load if the backend omits serviceAccountKeyJson (empty-string fallback).
• File details: when file.uri is present, Conduit URI renders above the existing URL block; copy button toasts URI copied to clipboard.
• File details: download / open / preview / URL copy still use getFileUrl and are unchanged when uri is absent.
• AWS / Azure / Aliyun / Local fields and provider list are unchanged.

Local verification

• pnpm exec tsc --noEmit passes
• pnpm exec eslint on the five files: no errors (pre-existing @next/next/no-img-element warning in FileDetailsSheet)
• FormSchema cases: ADC omitted/empty, path-only, JSON-only succeed; AWS min(5) unchanged

Live Storage settings / File details against a Conduit instance running #1509 was not available in this environment.

Scope

Only these files:

• src/lib/models/storage/settings.ts
• src/components/storage/settings/zod.ts
• src/components/storage/settings/settingsForm.tsx
• src/lib/models/storage/schemas.ts
• src/components/storage/browse/FileDetailsSheet.tsx

Draft until backend #1509 lands and this is manually verified against a live storage module.