Distinguish price loading/unavailable, fix analytics 0-flash, surface silent save failures (#674-#677)

[Kingsman-99]

• Distinguish loading vs. unavailable price state in use-token-price.ts consumers #675: audited all 5 consumers of `use-token-price.ts`. Fixed two real gaps — `stream-card.tsx` rendered loading and unavailable identically (both showed nothing); now shows a skeleton pulse while loading. `create-form.tsx`'s "Fetching price…" indicator was dead code (nested inside a block that can only render once the price has already resolved, so `priceLoading` was always false there) — moved it out so it's actually reachable, and added a distinct "Price unavailable" message for the resolved-but-null case. `dashboard-stats.tsx` already handled this correctly; `create-confirmation.tsx` and the stream detail page only use the price for an XLM-denominated fee estimate that never renders a USD value, so there's nothing to distinguish there.
• Fix analytics page stat cards flashing 0 during initial load #674: `analytics/page.tsx` called `useStreams({ enablePolling: false })` but never destructured `loading`, so the four stat cards flashed "0" before real data resolved. Destructured it and render a skeleton pulse per card while loading. (`hooks/use-streams.ts` had the same pre-existing corruption fixed elsewhere this session — two competing implementations merged together, duplicate declarations, two conflicting `return` statements — reconciled into one, since it directly blocked `loading` from working at all here.)
• Surface use-form-draft.ts's silent save failures to the user #676: `use-form-draft.ts`'s `save()` silently discarded quota/unavailable errors. Added an optional `onSaveError` callback (fires once per failure streak, resets on the next successful save) and wired `create-form.tsx` to show a toast warning.
• Wrap use-webhooks.ts's unguarded localStorage.setItem calls in try/catch #677: `use-webhooks.ts`'s `saveWebhooks`/`saveHistory` called `localStorage.setItem` unguarded — wrapped both in try/catch (returning a success flag) matching `use-form-draft.ts`'s pattern, and added the same `onSaveError` callback convention, wired to a toast in `webhook-settings.tsx`.

Closes #674
Closes #675
Closes #676
Closes #677

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