fix: polish completion errors and rejected number fields

[chhoumann]

Why

Three loose ends from the audit. On QuickAdd before 2.31 the [[ and # pickers showed the Obsidian CLI's raw "Command not found" text. A number field that failed validation looked empty while its error said "Between 1 and 5". Quick Capture had not been run live since the capture refactor in #6.

What changed

• suggest.ts maps the CLI's "Command "quickadd:suggest" not found" text to "Link and tag completion needs QuickAdd 2.31 or later." Other errors pass through. The pickers' empty view shows it.
• Number fields are now controlled, like text fields. Raycast clears an uncontrolled text field when the form re-renders with its error, so a rejected value vanished from view.
• README and ARCHITECTURE now say completion needs QuickAdd 2.31.

Scope

No change to Quick Capture. It was run live and works as is.

Verification

• Unit test for the mapping: a not-found text maps, Vault not found. passes through. It fails with the mapping removed.
• Number field, live against e2e-number. Before the fix, a 9 typed at +0.76 s and at +4.1 s showed in the field. After submit the field read empty next to "Between 1 and 5". So the keystroke was not dropped; the error re-render cleared it. After the fix the field keeps 9 beside the error. Correcting it to 3 and submitting wrote - rating: 3 to Output/Inbox.md.
• Quick Capture, live: the deeplink with a text argument and the e2e vault in its context wrote - text: polish quick capture 2114 to Output/Inbox.md. The toast read "Added to Output/Inbox.md".
• Not verified live: the picker message against QuickAdd 2.30. Swapping the e2e vault's plugin bundle was not permitted in this session.
• pnpm lint, pnpm test (76 passed), tsc --noEmit, pnpm build, and pnpm e2e:protocol (13 passed) are green.