fix: move swarm stacks to be under projects

[kmendell]

Checklist

• This PR is not opened from my fork’s main branch

What This PR Implements

Fixes: #2226

Changes Made

Testing Done

• Development environment started: ./scripts/development/dev.sh start
• Frontend verified at http://localhost:3000
• Backend verified at http://localhost:3552
• Manual testing completed (describe):
• No linting errors (e.g., just lint all)
• Backend tests pass: just test backend

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Greptile Summary

This PR introduces a new "Swarm Stack Projects" concept that persists stack metadata in a database table (swarm_stack_projects) and reorganises the UI so that saved stacks live under the Projects section rather than the Swarm/Stacks runtime view. The change separates "live runtime" (Swarm → Stacks) from "saved compose files" (Projects → Swarm), with a new "Down" action for the runtime view and a full editor in the Projects view.

• Adds migration 051, the SwarmStackProject model, five new API endpoints (list/get/update/delete stackprojects, down stack), and the SyncStackProjectsFromFileSystem reconciliation loop that keeps the DB in sync with the filesystem on every read.
• Replaces the old filesystem-traversal listPersistedStackSourcesInternal with DB-backed queries, and introduces GetStackProject/UpsertStackProject/DeleteStackProject service methods consumed by a new SwarmProjectEditor Svelte component.
• Moves dockerSocketPathInternal and related helpers to a Linux-only build file, eliminating the dead no-op stubs on non-Linux platforms.

Confidence Score: 4/5

Safe to merge with awareness of a known concurrency issue in the upsert path that can surface as opaque 500 errors under concurrent writes to the same stack name.

The core logic is sound and the DB migration, model, and service layer are well-structured. The outstanding concurrency issue in upsertStackProjectRecordInternal (select-then-insert without atomicity) identified in a prior review round remains unaddressed; under concurrent saves to the same stack name it produces a unique-constraint violation that surfaces as a 500. New findings in this pass are non-blocking performance concerns: GetStackProject triggers a full filesystem sync twice per call (once directly, once through GetStackSource), which compounds with UpsertStackProject calling GetStackProject.

backend/internal/services/swarm_service.go — the upsert and GetStackProject/GetStackSource call chain warrant a second look before shipping to production workloads with many stacks or concurrent users.

Prompt To Fix All With AI

Fix the following 3 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 3
backend/internal/services/swarm_service.go:1301-1325
**Redundant full filesystem sync on every `GetStackProject` call**

`GetStackProject` calls `getStackProjectRecordInternal(ctx, …, true)` (triggering `SyncStackProjectsFromFileSystem`), then immediately calls `GetStackSource`, which itself calls `getStackProjectRecordInternal(ctx, …, true)` a second time — causing another full sync. Each sync scans all stack directories, stats compose/env files, parses YAML via `countStackProjectServicesFromComposeInternal`, and runs upsert queries for every stack. With many stacks this doubles the I/O and DB cost of every `GetStackProject` (and by extension `UpsertStackProject`, which calls `GetStackProject`). The second sync is guaranteed to see an already-up-to-date DB since the first sync just ran; passing `sync=false` on the inner call, or reading the compose content directly from `stackProject.Path` instead of delegating to `GetStackSource`, would eliminate the redundancy.

### Issue 2 of 3
backend/internal/services/swarm_service.go:2557-2559
Unnecessary temp copy for `DirName` pointer — the project-style `new(expr)` helper (used elsewhere, e.g. `base.go`) removes the need for the intermediate `dirNameCopy` variable.

```suggestion
	dirName := filepath.Base(stackSourceDir)
	serviceCount, serviceCountErr := s.countStackProjectServicesFromComposeInternal(ctx, environmentID, stackName, stackSourceDir)
```

### Issue 3 of 3
backend/internal/services/swarm_service.go:2571
Update `DirName` to use `new(dirName)` after removing the `dirNameCopy` intermediate variable.

```suggestion
		DirName:       new(dirName),
```

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[kmendell]

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[kmendell]

• fix: move swarm stacks to be under projects #2234 👈 (View in Graphite)
• main

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[getarcaneappbot]

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