refactor(update)!: make obtainability a property of updates, not a surface

The owner could not tell from the UI what "Buzz Price Tracking" enabled, what the
"Price alert threshold" number meant, or what "Price Alerts" was alerting about.
That was not a copy problem: the implementation exposed our mechanism (a page
scrape) and our SQL predicates as the user's concepts. Two concrete defects came
from the same root:

- the alert population included versions the user already owns (neither the event
  generator nor the query filtered on is_in_library; in the owner's library 28 of
  52 gated versions were already downloaded, so most "alerts" were about files
  already on disk, which cannot become cheaper *for them*);
- a threshold-filtered state list lived in a notification surface, so an empty
  panel had three indistinguishable causes and read as a broken feature.

The information model is now the version plus ownership: cost is shown only where
a decision exists. Owned -> nothing. Not owned and free -> nothing. Not owned and
gated -> the price when it is known, `Paid` without a number when it is not, and
early access keeps its countdown because "free on <date>" decides between waiting
and paying. The numeric threshold has no place in that model: every decision is
categorical (wait / pay / skip), so the setting, the comparison and the whole
alert-state machine are gone.

- both alert-state columns are removed from the schema rather than left dead; a
  database created by an unreleased build has them dropped on open (native
  ALTER TABLE ... DROP COLUMN, guarded), which is a no-op for everyone else
- gate events are emitted only for versions the user does not have, and the
  price-drop event goes with the threshold it belonged to
- both alert endpoints, PriceAlertsHandler and the service-registry adapter field
  it needed are removed: events already reach the UI through the refresh response
- the bell tab, panel, CSS, both entry points, the unread watermark and their
  locales are removed; the setting keeps only the enable flag and the refresh
  interval and is framed as plumbing
- "Price unavailable" is replaced by `Paid`: the gate is certain from the public
  API, only the number is best-effort, and that is our plumbing, not the user's
  problem

Verified against a copy of the owner's real database: 52 gated versions ->
28 owned (now silent) + 24 the feature is actually about; the drop migration ran
and both removed endpoints 404.

tests/frontend/components/modelVersionsTab.downloadButton.test.js

@@ -284,7 +284,7 @@ describe('ModelVersionsTab download button visibility', () => {
   });
 });
 
-describe('ModelVersionsTab price badges', () => {
+describe('ModelVersionsTab obtainability badges', () => {
   let getModelApiClient;
   let fetchModelUpdateVersions;
 
@@ -316,63 +316,83 @@ describe('ModelVersionsTab price badges', () => {
     return document.querySelector(`.model-version-row[data-version-id="${versionId}"]`);
   }
 
-  it('shows the price for a gated version whose price was captured', async () => {
+  function renderOne(version) {
     fetchModelUpdateVersions.mockResolvedValue(buildRecord([
       {
-        versionId: 20,
-        name: 'Alpha',
+        versionId: 1,
+        name: 'v1',
         isInLibrary: false,
         shouldIgnore: false,
-        isPaid: true,
-        paidAccess: { permanent: true, endsAt: null },
-        priceBuzz: 5000,
-        listPriceBuzz: 5000,
-        priceCheckedAt: 1791039694.5,
-        priceAttemptedAt: 1791039694.5,
+        ...version,
       },
     ]));
+    return renderVersions();
+  }
 
-    await renderVersions();
+  const PAID_GATE = { permanent: true, endsAt: null };
 
-    expect(rowFor(20).textContent).toContain('5,000 Buzz');
+  it('shows the download price for a paid version the user does not have', async () => {
+    await renderOne({ isPaid: true, paidAccess: PAID_GATE, priceBuzz: 5000 });
+
+    expect(rowFor(1).textContent).toContain('5,000 Buzz');
   });
 
-  it('marks a gated version with no readable price as unavailable', async () => {
-    // The mature-model case: we looked, no host would serve the page.
-    fetchModelUpdateVersions.mockResolvedValue(buildRecord([
-      {
-        versionId: 21,
-        name: 'Beta',
-        isInLibrary: false,
-        shouldIgnore: false,
-        isPaid: true,
-        paidAccess: { permanent: true, endsAt: null },
-        priceBuzz: null,
-        priceAttemptedAt: 1791039694.5,
-      },
-    ]));
+  it('says Paid without a number when the price could not be read', async () => {
+    // The gate is certain (it comes from the public API); only the number is
+    // best-effort, and that is our plumbing rather than the user's problem.
+    await renderOne({ isPaid: true, paidAccess: PAID_GATE, priceBuzz: null });
 
-    await renderVersions();
-
-    expect(rowFor(21).textContent).toContain('Price unavailable');
+    expect(rowFor(1).textContent).toContain('Paid');
+    expect(rowFor(1).textContent).not.toContain('Buzz');
   });
 
-  it('stays quiet when the price was never looked up', async () => {
-    fetchModelUpdateVersions.mockResolvedValue(buildRecord([
-      {
-        versionId: 22,
-        name: 'Gamma',
-        isInLibrary: false,
-        shouldIgnore: false,
-        isPaid: true,
-        paidAccess: { permanent: true, endsAt: null },
-        priceBuzz: null,
-        priceAttemptedAt: null,
-      },
-    ]));
+  it('shows the early access countdown alongside the price', async () => {
+    await renderOne({
+      isEarlyAccess: true,
+      earlyAccessEndsAt: new Date(Date.now() + 3 * 86400000).toISOString(),
+      paidAccess: { permanent: false, endsAt: '2999-01-01T00:00:00.000Z' },
+      priceBuzz: 500,
+    });
 
-    await renderVersions();
+    const text = rowFor(1).textContent;
+    expect(text).toContain('Early Access');
+    expect(text).toContain('500 Buzz');
+  });
 
-    expect(rowFor(22).textContent).not.toContain('Price unavailable');
+  it('shows nothing about cost for a version already in the library', async () => {
+    // A version on disk cannot become cheaper *for this user*.
+    await renderOne({
+      isInLibrary: true,
+      isPaid: true,
+      paidAccess: PAID_GATE,
+      priceBuzz: 5000,
+      gateLapsedAt: '2026-09-28T00:00:00.000Z',
+    });
+
+    const text = rowFor(1).textContent;
+    expect(text).not.toContain('Buzz');
+    expect(text).not.toContain('Paid');
+    expect(text).not.toContain('Free Now');
+    expect(text).toContain('In Library');
+  });
+
+  it('marks a version that became free and is not in the library', async () => {
+    await renderOne({
+      isInLibrary: false,
+      isPaid: false,
+      priceBuzz: null,
+      gateLapsedAt: '2026-09-28T00:00:00.000Z',
+    });
+
+    expect(rowFor(1).textContent).toContain('Free Now');
+  });
+
+  it('shows nothing at all for a plain free version', async () => {
+    await renderOne({ isInLibrary: false, isPaid: false, priceBuzz: null });
+
+    const text = rowFor(1).textContent;
+    expect(text).not.toContain('Buzz');
+    expect(text).not.toContain('Paid');
+    expect(text).not.toContain('Free Now');
   });
 });