fix(a11y): add ARIA progressbar to QuotaBar component (#1878)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - Operators run those agents against paid model providers, so the web
UI has a Costs surface that reports spend and quota utilisation
> - Those figures are drawn as horizontal bars by the shared `QuotaBar`
component (`ui/src/components/QuotaBar.tsx`), consumed by
`BillerSpendCard` and `ProviderQuotaCard`
> - `QuotaBar` renders its fill as a plain `<div>` whose CSS width is
the only encoding of the percentage — no `role`, no value attributes, no
accessible name
> - A screen reader therefore announces nothing at all for these bars,
so the spend and quota numbers they convey are unavailable to
assistive-technology users (WCAG 2.1 SC 4.1.2, Name/Role/Value)
> - The same gap is being closed for the other bars in this area by
#1805 (BudgetPolicyCard) and #1869 (ProviderQuotaCard's inline bars);
`QuotaBar` is the remaining shared component with no ARIA semantics
> - This pull request adds the standard ARIA progressbar attributes to
`QuotaBar`'s fill element, reusing the `label` prop the component
already takes
> - The benefit is that every progress bar on the Costs screen exposes
its name and current value to assistive technology, with no visual or
behavioural change for sighted users

## Linked Issues or Issue Description

No existing GitHub issue — the problem is described in-PR below,
following [`bug_report.yml`](.github/ISSUE_TEMPLATE/bug_report.yml).

Related PRs from the same accessibility sweep (each covers a *different*
component, so these are companions rather than duplicates — all three
are currently open):

- Refs #1805 — ARIA attributes for the BudgetPolicyCard progress bar
- Refs #1869 — ARIA attributes for the ProviderQuotaCard inline bars

**What happened?**
On the Costs screen, the spend/quota bars rendered by `QuotaBar` (via
`BillerSpendCard` and `ProviderQuotaCard`) are non-semantic `<div>`
elements. Screen readers skip them entirely: no role, no value, no label
is announced, so the percentage information is available only visually.

**Expected behavior**
Each bar should be exposed as a progress bar with an accessible name and
its current value — e.g. announced as "Weekly spend: 45%, progress bar".

**Steps to reproduce**
1. Run the app and open the Costs page.
2. Expand any provider or biller card so a quota/spend bar is visible.
3. Navigate to the bar with a screen reader (VoiceOver, NVDA, or Chrome
DevTools → Accessibility pane).
4. Observe that the fill element has no role, no value, and no
accessible name.

**Paperclip version or commit**
Reproduces on `master`; `ui/src/components/QuotaBar.tsx` has carried no
ARIA attributes since the component was introduced.

**Deployment mode**
Not deployment-specific — the missing markup is in the shipped
component. Verified in local dev (`pnpm dev`).

**Agent adapter(s) involved**
Not adapter-specific (core UI).

## What Changed

- `ui/src/components/QuotaBar.tsx`: added `role="progressbar"` to the
fill `<div>`.
- Added `aria-valuenow={Math.round(clampedPct)}` with
`aria-valuemin={0}` / `aria-valuemax={100}`, using the already-clamped
percentage so the reported value can never fall outside 0–100.
- Added an `aria-label` of the form `<label>: <pct>%`, reusing the
existing `label` prop for the accessible name.
- No changes to props, styling, layout, or rendering logic: 1 file, 5
added lines, 0 deleted.

## Verification

- Manual: open Costs → expand a provider/biller card, inspect the bar in
Chrome DevTools → Accessibility pane. The fill node now reports role
`progressbar`, value `45`, min `0`, max `100`, and name "Weekly spend:
45%".
- Manual: with VoiceOver/NVDA, the bar announces "Weekly spend: 45%,
progress bar" instead of being skipped.
- Visual regression check: the bar is unchanged for sighted users — only
ARIA attributes were added, no class or style changes.
- CI (lint, typecheck, build, tests) is green on this branch.
- No unit test is added: the change is a set of static ARIA attributes
on one element, and `QuotaBar` currently has no test file. Happy to add
one if maintainers would like coverage here.

## Risks

Low risk. Presentation-only accessibility metadata on a single element;
no props, state, or styling change, and no other component is touched.
The one debatable point is that the percentage appears in both
`aria-label` and `aria-valuenow`, so some screen readers may announce it
twice; both forms are valid, and the label is kept because it carries
the bar's name alongside the value. Happy to drop the percentage from
the label if reviewers prefer the terser announcement.

## Model Used

<!-- @bluzername: please replace this line with the provider + exact
model ID (and context window / reasoning mode if relevant), or "None —
human-authored". Required by CONTRIBUTING.md. -->

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [ ] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [ ] I have run tests locally and they pass
- [ ] I have added or updated tests where applicable
- [ ] I have updated relevant documentation to reflect my changes (no
docs cover this component's markup)
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [ ] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

ui/src/components/QuotaBar.tsx

@@ -46,6 +46,11 @@ export function QuotaBar({
       <div className="relative h-2 w-full border border-border overflow-hidden">
         {/* fill */}
         <div
+          role="progressbar"
+          aria-valuenow={Math.round(clampedPct)}
+          aria-valuemin={0}
+          aria-valuemax={100}
+          aria-label={`${label}: ${Math.round(clampedPct)}%`}
           className={cn(
             "absolute inset-y-0 left-0 transition-(--tp-width-background-color) duration-150",
             fillColor(clampedPct),