quak backup --verify re-hashes stored originals and downloads again any that do not match (closes #168)

`--verify`, or `lib.backup({ verify: true })`, hashes each original already
at its save path as the download check does, streamed, a live photo as
`<imageHash>:<videoHash>`. A mismatch is logged, removed and put back in the
same run, and what is put back is hashed too, since a copy from the content
cache is not checked; one that still does not match, or a failed fetch, goes
into `failures.json`. A file with no recorded hash counts as unchecked. The
result, the summary and `--json` gain `verified`, `mismatched` and
`unchecked`.

Judgement call: a stored original that cannot be read for hashing is recorded as failed and left in place.
Judgement call: a copy put back that still does not match stays at its save path and is not counted as downloaded.
Judgement call: the summary prints the three counts only with `--verify`.

Model: opus-5-5

src/cli-commands.ts

@@ -402,7 +402,7 @@ export const backupMetadataCommand = async (
 export const backupCommand = async (
     ctx: CliContext,
     dir: string,
-    opts: { json?: boolean },
+    opts: { json?: boolean; verify?: boolean },
 ): Promise<number> => {
     await init();
     const client = requireSession(ctx);
@@ -433,6 +433,7 @@ export const backupCommand = async (
             const result = await lib.backup({
                 downloadDirectory: dir,
                 lockHeld: true,
+                verify: opts.verify,
                 onProgress: (msg) => {
                     if (!opts.json) ctx.stderr.write(msg + "\n");
                 },
@@ -445,6 +446,11 @@ export const backupCommand = async (
                 ctx.stderr.write(`  Total files: ${result.totalFiles}\n`);
                 ctx.stderr.write(`  Downloaded:  ${result.downloaded}\n`);
                 ctx.stderr.write(`  Skipped:     ${result.skipped}\n`);
+                if (opts.verify) {
+                    ctx.stderr.write(`  Verified:    ${result.verified}\n`);
+                    ctx.stderr.write(`  Mismatched:  ${result.mismatched}\n`);
+                    ctx.stderr.write(`  Unchecked:   ${result.unchecked}\n`);
+                }
                 ctx.stderr.write(`  Failed:      ${result.failed}\n`);
                 if (result.errors.length > 0) {
                     ctx.stderr.write("\nFailed files:\n");