feat(core,stream,meta,app,android,cli): sign in to Proton and sync watch history

A Proton account is now optional alongside public links. Signing in (password,
then a second-factor code and a mailbox password where the account has them;
a CAPTCHA gate is solved in the Android app) stores one session blob in the OS
credential store under `proton-account`, writing back every refreshed token
since refresh tokens are single-use. With an account, folders of the viewer's
own Drive — My Files, other devices, shared with me — can be added as shares
through the same `ShareClient` surface as a public link.

Watch history syncs through a `proton-stream` device in that Drive: one
`watch-history/<installation>.json` per installation, so no two devices ever
write the same file. Each sync reads the others and merges per episode, newer
`updated_at` wins, with a deterministic tie-break. It runs at launch, after
sign-in, whenever the player closes and every five minutes. A session that can
no longer refresh signs the app out instead of failing on every launch.

The CLI gains `login`, `logout`, `account`, `browse` and `sync`.

Also in this change:
- Android offline downloads no longer look stuck (B64): two transfer at once,
  through a copy stream with no read-ahead, with a smoothed transfer rate.
- Choosing a metadata match by hand now enriches the title too, instead of
  keeping the old match's episodes and artwork.

The catalog schema is unchanged.

android/app/src/test/java/io/narl/protonstream/download/TransferRateTest.kt

@@ -0,0 +1,37 @@
+package io.narl.protonstream.download
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class TransferRateTest {
+    @Test
+    fun `the first sample has no rate to report`() {
+        assertEquals(0L, TransferRate().sample(4L * 1024 * 1024, 1_000))
+    }
+
+    @Test
+    fun `a steady transfer reports its rate`() {
+        val rate = TransferRate()
+        rate.sample(0, 0)
+        assertEquals(1_000_000L, rate.sample(1_000_000, 1_000))
+        assertEquals(1_000_000L, rate.sample(2_000_000, 2_000))
+    }
+
+    @Test
+    fun `one slow block moves the rate without halving it`() {
+        val rate = TransferRate()
+        rate.sample(0, 0)
+        rate.sample(1_000_000, 1_000)
+        val after = rate.sample(2_000_000, 3_000)
+        assertTrue(after in 600_000L..999_999L)
+    }
+
+    @Test
+    fun `a resumed download starting below the last sample starts over`() {
+        val rate = TransferRate()
+        rate.sample(0, 0)
+        rate.sample(1_000_000, 1_000)
+        assertEquals(1_000_000L, rate.sample(0, 2_000))
+    }
+}

android/app/src/test/java/io/narl/protonstream/ui/AccountUiTest.kt

@@ -0,0 +1,38 @@
+package io.narl.protonstream.ui
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class AccountUiTest {
+    @Test
+    fun `the sync line says how long ago and what came in`() {
+        val minute = 60_000L
+        assertEquals("Watch history syncs with your Drive", syncLine(AccountUiState(), 0))
+        assertEquals("Synced just now", syncLine(AccountUiState(syncedAt = 0), 30_000))
+        assertEquals("Synced 5 min ago", syncLine(AccountUiState(syncedAt = 0), 5 * minute))
+        assertEquals(
+            "Synced 2 h ago · 3 from other devices",
+            syncLine(AccountUiState(syncedAt = 0, applied = 3), 120 * minute),
+        )
+    }
+
+    @Test
+    fun `a failed sync is said in place of when it last worked`() {
+        assertEquals(
+            "Watch history did not sync: offline",
+            syncLine(AccountUiState(syncedAt = 0, syncError = "offline"), 0),
+        )
+    }
+
+    @Test
+    fun `the verification page may only navigate within Proton over https`() {
+        assertTrue(isProtonPage("https", "verify.proton.me"))
+        assertTrue(isProtonPage("https", "proton.me"))
+        assertFalse(isProtonPage("http", "verify.proton.me"))
+        assertFalse(isProtonPage("https", "proton.me.example.com"))
+        assertFalse(isProtonPage("https", "notproton.me"))
+        assertFalse(isProtonPage("https", null))
+    }
+}