Add service information feature with version checks

This commit introduces a new "Service Information" section displaying runtime details, installed version, and update status for the NexaPG application. It includes backend API endpoints, database schema changes, and a corresponding frontend page that allows users to check for updates against the official repository. The `.env` example now includes an `APP_VERSION` variable, and related documentation has been updated.

backend/app/services/service_info.py

@@ -0,0 +1,111 @@
+import asyncio
+import json
+import re
+from datetime import datetime, timezone
+from urllib.error import URLError
+from urllib.request import Request, urlopen
+
+UPSTREAM_REPO_WEB = "https://git.nesterovic.cc/nessi/NexaPG"
+UPSTREAM_REPO_API = "https://git.nesterovic.cc/api/v1/repos/nessi/NexaPG"
+
+
+def _extract_version(payload: str) -> str | None:
+    txt = payload.strip()
+    if not txt:
+        return None
+
+    try:
+        data = json.loads(txt)
+        if isinstance(data, dict):
+            for key in ("latest_version", "version", "tag_name", "name"):
+                value = data.get(key)
+                if isinstance(value, str) and value.strip():
+                    return value.strip()
+        if isinstance(data, list) and data and isinstance(data[0], dict):
+            for key in ("latest_version", "version", "tag_name", "name"):
+                value = data[0].get(key)
+                if isinstance(value, str) and value.strip():
+                    return value.strip()
+    except json.JSONDecodeError:
+        pass
+
+    first_line = txt.splitlines()[0].strip()
+    if first_line:
+        return first_line[:64]
+    return None
+
+
+def _parse_semver(value: str) -> tuple[int, ...] | None:
+    normalized = value.strip().lower()
+    if normalized.startswith("v"):
+        normalized = normalized[1:]
+    parts = re.findall(r"\d+", normalized)
+    if not parts:
+        return None
+    return tuple(int(p) for p in parts[:4])
+
+
+def is_update_available(current_version: str, latest_version: str) -> bool:
+    current = _parse_semver(current_version)
+    latest = _parse_semver(latest_version)
+    if current and latest:
+        max_len = max(len(current), len(latest))
+        current = current + (0,) * (max_len - len(current))
+        latest = latest + (0,) * (max_len - len(latest))
+        return latest > current
+    return latest_version.strip() != current_version.strip()
+
+
+def _get_json(url: str):
+    req = Request(url, headers={"User-Agent": "NexaPG/1.0"})
+    with urlopen(req, timeout=8) as response:
+        raw = response.read(64_000).decode("utf-8", errors="replace")
+    return json.loads(raw)
+
+
+def _fetch_latest_from_upstream_sync() -> tuple[str, str]:
+    latest_release_url = f"{UPSTREAM_REPO_API}/releases/latest"
+    tags_url = f"{UPSTREAM_REPO_API}/tags?page=1&limit=1"
+    commits_url = f"{UPSTREAM_REPO_API}/commits?sha=main&page=1&limit=1"
+
+    try:
+        release = _get_json(latest_release_url)
+        if isinstance(release, dict):
+            tag = (release.get("tag_name") or release.get("name") or "").strip()
+            if tag:
+                return tag[:64], "release"
+    except Exception:
+        pass
+
+    try:
+        tags = _get_json(tags_url)
+        if isinstance(tags, list) and tags:
+            first = tags[0] if isinstance(tags[0], dict) else {}
+            tag = (first.get("name") or "").strip()
+            if tag:
+                return tag[:64], "tag"
+    except Exception:
+        pass
+
+    commits = _get_json(commits_url)
+    if isinstance(commits, list) and commits:
+        first = commits[0] if isinstance(commits[0], dict) else {}
+        sha = (first.get("sha") or "").strip()
+        if sha:
+            short = sha[:7]
+            return f"commit-{short}", "commit"
+    raise ValueError("Could not fetch release/tag/commit from upstream repository")
+
+
+async def fetch_latest_from_upstream() -> tuple[str | None, str | None, str | None]:
+    try:
+        latest, ref = await asyncio.to_thread(_fetch_latest_from_upstream_sync)
+        return latest, ref, None
+    except URLError as exc:
+        return None, None, f"Version check failed: {exc.reason}"
+    except Exception as exc:  # noqa: BLE001
+        return None, None, f"Version check failed: {exc}"
+
+
+def utcnow() -> datetime:
+    return datetime.now(timezone.utc)