fix(icon): serve icons from cache and repair Docker Manager icon cache

[mstrhakr]

Docker Manager downloads net.unraid.docker.icon URLs verbatim, so an SVG
source left raw SVG bytes in -icon.png. The browser could not
render that file and fell back to question.png, which docker.json then
recorded permanently because DM only re-resolves an icon when the stored
path is missing.

• Store only verified PNG bytes in the plugin icon cache; reject any
  conversion result that is not a real PNG
• Serve IconCache.php strictly from the cache, populating only on miss,
  staleness, or corrupt entries, and keep the last good PNG when a
  refresh fails
• Replace Docker Manager icon files when missing, corrupt, or stale
  instead of skipping any existing file, using an atomic write
• Repoint docker.json at the seeded icon so Docker Manager stops using
  the label URL and stops sticking to question.png
• Seed every container matching an icon source whenever the cache is
  populated, and pass container context from the stack and dashboard
  views so both caches stay aligned
• Route http(s), data URI, and local /mnt icon sources through the cache
  proxy in PHP and JS
• Add tests for corrupt-file replacement and docker.json repair

Fixes #129

[Copilot]

🟡 Changes recommended

There are concrete reliability/concurrency issues in the new cache/seed file-writing logic (non-atomic cache writes and non-unique temp filenames) plus test cleanup gaps that should be addressed before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR hardens icon handling by ensuring only valid PNG bytes are cached/served, routing eligible icon sources through a cache proxy, and repairing Docker Manager’s icon cache/metadata so broken icons don’t permanently stick.

Changes:

• Add PNG validation + staleness rules to the icon cache, and serve icons strictly from cached PNGs via IconCache.php.
• Seed/repair Docker Manager icon files and docker.json metadata based on the plugin cache (including container-context routing from UI).
• Extend unit tests and test bootstrap constants to cover Docker Manager icon repair flows.

File summaries

File	Description
tests/unit/StackInfoTest.php	Adds tests for replacing corrupt DM icon files and repairing docker.json icon metadata; updates constants usage.
tests/bootstrap.php	Defines temp paths for Docker Manager icon RAM/persist dirs and docker.json in unit tests.
source/compose.manager/README.md	Removes “(Beta)” label from plugin name.
source/compose.manager/javascript/composeManagerMain.js	Routes eligible icon sources through IconCache.php and passes container context when available.
source/compose.manager/include/Util.php	Adds PNG detection/staleness helpers; enforces PNG-only caching; seeds/repairs Docker Manager icons and metadata.
source/compose.manager/include/Exec.php	Seeds Docker Manager icon cache during container icon resolution.
source/compose.manager/include/Defines.php	Adds constants for DM icon paths and the net.unraid.docker.icon label key.
source/compose.manager/IconCache.php	Serves only from cache, supports refresh, and optionally repairs DM icon cache/metadata for a container.
source/compose.manager/compose.manager.dashboard.page	Passes container name into composeIconSrc() so the cache proxy can repair DM cache.
compose.manager.plg	Updates version/pluginURL and changelog entry for the release.

Review details

Suppressed comments (2)

tests/unit/StackInfoTest.php:782

• This test replaces a corrupt RAM icon but doesn’t remove the corresponding persistent Docker Manager icon file that may also be created by compose_seed_docker_manager_icon(). Cleaning both locations keeps the test isolated.

        $this->assertTrue(compose_file_is_png($ramPath), 'corrupt Docker Manager icon must be replaced with real PNG');
        @unlink($ramPath);
    }

tests/unit/StackInfoTest.php:813

• This cleanup removes the RAM icon and docker.json, but compose_seed_docker_manager_icon() also writes a persistent icon file. Remove that as well to avoid cross-test pollution in the temp COMPOSE_DM_ICON_PERSIST_DIR.

        @unlink(COMPOSE_DM_ICON_RAM_DIR . '/' . $name . '-icon.png');
        @unlink(COMPOSE_DM_WEBUI_INFO_FILE);
    }

• Files reviewed: 10/10 changed files
• Comments generated: 4
• Review effort level: Lite

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