feat: add CI to generate OPC for OTA workflow (#15624)

# Description

Adds the CI half of the profile OTA pipeline: a push-triggered workflow
that
rebuilds a vendor's binary preset cache (`<vendor>.opc`) whenever its
profile
changes on `main` / `release/*`, and publishes it as a versioned release
asset
for OrcaCloud's OTA Manager to pick up.

### `.github/workflows/post_merge_profiles.yml` (new)

Push-triggered counterpart to `check_profiles.yml` (which only gates
PRs):

- Diffs the push to find which vendors under `resources/profiles/**`
changed.
- Reads the Orca version from `version.inc` and each vendor's 4-part
`version`
from `resources/profiles/<vendor>.json` (fails the run if it isn't
`A.B.C.D`).
- Downloads the prebuilt `generate_system_cache` from this repo's
`nightly-builds` release and builds one `<vendor>.opc` per changed
vendor.
- Packages each as
`<orca_ver>_<vendor>_<profile_version>_<UTCyyyymmddHHMM>.zip` (zip root
`<vendor>.opc`) — the asset-name contract OrcaCloud's release scanner
expects.
- Uploads them to a per-Orca-version release on the profiles repo via a
scoped
  GitHub App token.

It stops there: no changelog, no R2, no OTA webhook — a maintainer still
publishes from the OTA Manager. Job is guarded to
`OrcaSlicer/OrcaSlicer`;
workflow permissions are `contents: read` (the cross-repo write uses the
App
token only).

### `.github/workflows/build_orca.yml`

Two steps on the Linux leg: upload `generate_system_cache` as a CI
artifact,
and (on `main`) deploy it to the `nightly-builds` release as
`generate_system_cache_Linux_Ubuntu2404_nightly` so the workflow above
has a
tool to download. `.opc` is 64-bit little-endian and
platform-independent, so
only the Linux binary is shipped.

### `src/dev-utils/generate_system_cache.cpp`

New `-v` / `--vendor` option to generate the cache for a single vendor
(plus the
always-loaded Orca filament library) instead of all vendors, and an
error if the
named vendor produced no `.opc` (catches typos). Reuses
`PresetBundle::set_vendor_to_validate()` from #14217.

## Operational prerequisites

- Repo secrets `PROFILES_APP_ID` / `PROFILES_APP_PRIVATE_KEY` for a
GitHub App
  with `contents: write` on the target profiles repo.
- `env.PROFILES_OWNER` / `env.PROFILES_REPO` in
`post_merge_profiles.yml` must
  point at the production profiles repo OrcaCloud reads.
- `generate_system_cache_Linux_Ubuntu2404_nightly` only appears after
the first
post-merge nightly `build_orca` run; a profile-only push before then
fails at
  the download step.

## Screenshots/Recordings/Graphs

n/a — CI only.

## Tests

Exercised end-to-end in a staging environment: per-vendor `.opc` zips
published
in the expected `<orca_ver>_<vendor>_<profile_version>_<timestamp>.zip`
layout,
and `generate_system_cache -v <vendor>` confirmed to emit only that
vendor's
`.opc`.

[How to Download Pull Requests Artifacts for
Testing](https://www.orcaslicer.com/wiki/how_to_download_pr_artifacts)

src/dev-utils/generate_system_cache.cpp

@@ -23,7 +23,8 @@ int main(int argc, char* argv[])
 #else
         ("path,p", po::value<std::string>()->default_value("../../../resources/profiles"), "Path to profiles directory")
 #endif
-        ("log_level,l", po::value<int>()->default_value(2), "Log level (0=trace, 2=info, 4=error)");
+        ("log_level,l", po::value<int>()->default_value(2), "Log level (0=trace, 2=info, 4=error)")
+        ("vendor,v", po::value<std::string>()->default_value(""), "Vendor name. Optional; generate the cache for this vendor only (the Orca filament library is always included as the inheritance base). All vendors if not specified.");
     // clang-format on
 
     po::variables_map vm;
@@ -38,6 +39,7 @@ int main(int argc, char* argv[])
 
     const std::string profiles_path = vm["path"].as<std::string>();
     const int         log_level     = vm["log_level"].as<int>();
+    const std::string vendor        = vm["vendor"].as<std::string>();
 
     if (!fs::exists(profiles_path) || !fs::is_directory(profiles_path)) {
         std::cerr << "Error: '" << profiles_path << "' is not a valid directory\n";
@@ -59,8 +61,12 @@ int main(int argc, char* argv[])
     preset_bundle->set_is_validation_mode(true);
     preset_bundle->set_default_suppressed(true);
     preset_bundle->set_generate_vendor_caches(true);
+    // Empty == every vendor. Otherwise only this vendor (plus the always-loaded
+    // Orca filament library) is parsed, so only its <vendor>.opc is written.
+    preset_bundle->set_vendor_to_validate(vendor);
 
-    std::cout << "Loading system presets from: " << profiles_path << "\n";
+    std::cout << "Loading system presets from: " << profiles_path
+              << (vendor.empty() ? "" : " (vendor: " + vendor + ")") << "\n";
 
     try {
         // In validation mode data_dir() is the profiles directory set above, so the
@@ -71,6 +77,14 @@ int main(int argc, char* argv[])
         return 1;
     }
 
+    // A specific vendor must have produced its own cache; the always-loaded
+    // filament library alone would otherwise mask a misspelt or removed name.
+    if (!vendor.empty() && !fs::exists(fs::path(profiles_path) / (vendor + ".opc"))) {
+        std::cerr << "No cache was generated for vendor '" << vendor << "' under " << profiles_path
+                  << " - check the vendor name.\n";
+        return 1;
+    }
+
     size_t cache_count = 0;
     for (auto& entry : fs::directory_iterator(profiles_path))
         if (boost::iends_with(entry.path().string(), ".opc"))