Pending messages: show the translated note for capabilities_unknown on a held-copy resend #1809

Follow-up from #1808 (CodeRabbit thread on src/lib/ws.ts).

Repro path

1. The composer's pending list holds a held copy: a message kept after a send that did not go.
2. The page reconnects. Before the bridge's snapshot arrives (a slow link or a busy PC), the user presses Send now on the held copy.
3. useComposerSends.ts (~157-173) sends it again through submitComposerMessage, which goes to HerdrSocket.submit. That waits SNAPSHOT_WAIT_MS (2 s), then returns capabilities_unknown (fix(composer): name a late capability snapshot, not a dropped connection, in the not-sent note #1808). The row records { code: "capabilities_unknown", message: "this PC has not said yet what it supports; nothing was sent" }. The row is not marked uncertain: submitNotTyped lists the code.
4. src/components/PendingMessages.tsx (~79-80) uses submitNote only for input_draft, held_input, not_transmitted, rewind_dialog_open and first_message_unattended. Every other code shows t("Not sent: {message}") with the result's English message. A Korean, Japanese or Chinese page therefore shows the English sentence after its translated "Not sent:" prefix, not the note fix(composer): name a late capability snapshot, not a dropped connection, in the not-sent note #1808 added in src/lib/i18n/composer.{ko,ja,zh}.ts.

Change needed

• Add "capabilities_unknown" to that code list in src/components/PendingMessages.tsx, so the row shows submitNote("capabilities_unknown", …).
• Cover it in src/components/PendingMessages.test.tsx: a held row that failed with capabilities_unknown shows the translated note, not the English message.

Relation to #1795

Open PR #1795 changes src/components/PendingMessages.tsx and src/components/PendingMessages.test.tsx. This change waits for #1795 to merge, or can be folded into it. #1808 does not touch the file.