exif: GET /image/exif/full — exiftool dump for the DETAILS modal

The curated `image_exif` columns are a small slice of what exiftool
can read (camera/lens/GPS/capture/dates). Apollo's DETAILS modal wants
to surface everything — white balance, metering, MakerNotes, IPTC,
ICC profile, Composite tags, the lot — for an operator inspecting a
photo's provenance.

`read_full_exif_via_exiftool(path)` shells out to `exiftool -j -G -n`:
JSON output, group-prefixed keys (`EXIF:Make`, `MakerNotes:LensInfo`),
numeric values (callers can reformat). Spawned via web::block to keep
it off the actix worker — RAW with rich MakerNotes can take a few
seconds.

The endpoint is on-demand only; the indexer / file watcher does NOT
call it. Falls back to 503 with a clear message when exiftool isn't
on PATH so Apollo can render an "install exiftool" hint. Multi-library
union resolution mirrors set_image_gps / get_file_metadata.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/exif.rs

@@ -71,6 +71,53 @@ fn read_jpeg_at_ifd(exif: &exif::Exif, path: &Path, ifd: In) -> Option<Vec<u8>>
     Some(buf)
 }
 
+/// Shell out to `exiftool -j -G -n <path>` and return the per-file tag map.
+///
+/// `-j` requests JSON; the response is always an array of one element per
+/// input path. `-G` prefixes each key with the group name (`EXIF:Make`,
+/// `MakerNotes:LensInfo`, `File:FileSize`, …) so a UI can group the dump.
+/// `-n` returns numeric / raw values rather than exiftool's pretty-printed
+/// human strings, which keeps the output stable for clients that want to
+/// reformat (e.g. divide a focal-length numerator/denominator).
+///
+/// Returns:
+///  - `Ok(Some(value))` — the parsed object for this file.
+///  - `Ok(None)` — exiftool ran but the array was empty / not an object.
+///  - `Err(_)` — exiftool isn't on PATH, the spawn failed, or its stderr
+///    indicates an unsupported file. Caller surfaces a 503 / 422.
+///
+/// Used by `GET /image/exif/full` to power Apollo's DETAILS modal "FULL
+/// EXIF" pane. Per-file shell-out is fine for this on-demand surface;
+/// the indexer does NOT call this on the hot path (kamadak-exif covers
+/// the indexed columns; exiftool is the slow-path preview helper).
+pub fn read_full_exif_via_exiftool(path: &Path) -> Result<Option<serde_json::Value>> {
+    let output = Command::new("exiftool")
+        .arg("-j")
+        .arg("-G")
+        .arg("-n")
+        .arg(path)
+        .output()
+        .map_err(|e| anyhow!("exiftool spawn failed (is it on PATH?): {}", e))?;
+
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        return Err(anyhow!(
+            "exiftool exited with {}: {}",
+            output.status,
+            stderr.trim()
+        ));
+    }
+
+    let parsed: serde_json::Value = serde_json::from_slice(&output.stdout)
+        .map_err(|e| anyhow!("exiftool returned non-JSON output: {}", e))?;
+
+    // `-j` always wraps the result in an array — pull out the first object.
+    let arr = parsed
+        .as_array()
+        .ok_or_else(|| anyhow!("expected JSON array from exiftool -j"))?;
+    Ok(arr.first().cloned())
+}
+
 /// Tags exiftool exposes for embedded JPEG previews, in priority order. The
 /// largest valid JPEG returned by any of them wins. Different camera makers
 /// stash their largest preview under different names: Nikon's full-res