refactor(workspaces): split workspace_repos into git_repos + workspace_projects

[dvcdsys]

Rewrites the workspaces feature so the data model matches the words
operators use about it: projects are the canonical entity, workspaces
are pure aggregations of projects. The previous workspace_repos table
conflated clone metadata, workspace membership, and an owned-vs-linked
flag into one row, which forced increasingly awkward workarounds for
standalone repos and local-path projects.

What changed

Data model

projects              (canonical entity — unchanged)
git_repos             NEW — clone + webhook metadata, 1:1 with projects
                      for external repos only. Local projects have no
                      git_repos row at all.
workspace_projects    NEW — many-to-many junction (workspace_id ↔ project_path).
                      Adding to a workspace = INSERT here, removing =
                      DELETE. The project itself is untouched.
workspace_repos       DROPPED

projects.host_path is the single identity. Deleting a project
cascades to git_repos AND workspace_projects via FK ON DELETE
CASCADE.

API

Endpoint	Purpose
POST /api/v1/git-repos	Create an external project (clones + indexes; standalone, no workspace)
GET /api/v1/projects/{hash}/git-repo	Clone+webhook metadata
GET /api/v1/projects/{hash}/webhook-info	Webhook URL + secret
POST /api/v1/projects/{hash}/reindex	Manual re-clone+reindex
GET /api/v1/workspaces/{id}/projects	List projects in workspace
POST /api/v1/workspaces/{id}/projects	Link an indexed project
DELETE /api/v1/workspaces/{id}/projects/{hash}	Unlink (does not delete project)
POST /api/v1/webhooks/github/{hash}	Webhook now keyed by projects.path_hash

All previous /workspaces/{id}/repos[/...] endpoints are gone.

Webhook clean break

Webhook URLs now use projects.path_hash (stable across the system
and meaningful in logs). Operators with auto-registered GitHub hooks
must re-register or update the URL in GitHub's webhook settings.
On-disk clone directories are renamed during the migration from
{DataDir}/repos/{workspace_repos.id} to {DataDir}/repos/{path_hash},
so the indexed content survives.

Migration

migrateSplitWorkspaceRepos runs once at startup. For every legacy
workspace_repos row it:

1. Pre-seeds the matching projects row if absent (covers
   pending/cloning rows whose projects row hadn't been written yet).
2. Inserts a workspace_projects membership.
3. Inserts a git_repos row for owned external rows only (linked
   rows reuse the canonical owner; local rows have no git_repos at all).
4. Renames the on-disk clone dir.
5. DROPs the legacy table.

Idempotent — re-running boots after a successful migration is a no-op.

Dashboard

• WorkspaceDetailPage reads projects via /workspaces/{id}/projects.
  Project rows render via the new WorkspaceProjectRow with a single
  action: Unlink. Reindex / webhook config / delete live on the
  project's own detail page.
• AddRepoDialog.workspaceID is optional:
  • Provided → chains POST /git-repos with POST /workspaces/{id}/projects
    so the new project is linked into the current workspace.
  • Omitted → just creates a standalone project (mounted on /projects).
• AddExistingProjectDialog no longer disables local-path projects —
  they're regular workspace_projects rows now.

Tests

• go test ./... — all packages green.
• New gitrepos package tests (Create + UNIQUE + GetByHash + cascade).
• New workspaceprojects package tests (Link + duplicate + non-indexed +
  cascade).
• New HTTP tests: TestAddGitRepo_Succeeds, _Duplicate,
  TestReindexProject_RequiresGitRepo,
  TestDeleteProject_CascadesGitRepoAndMembership,
  TestLinkProjectToWorkspace_*, TestUnlinkProject.
• TestMigrate_SplitWorkspaceRepos seeds the legacy table (owned +
  linked + local rows) plus on-disk clone dirs, opens via
  OpenWith(DataDir), and asserts the table is dropped, git_repos +
  workspace_projects populated correctly, and the clone dir renamed.
• Existing webhooks_test.go + workspacesearch_test.go ported to
  the new model.
• Dashboard npm run build clean against regenerated generated.ts.

E2E (manual)

• Boot against a snapshot of the current dev DB. Confirm boot log
  reports the split migration ran, PRAGMA table_info(git_repos)
  and (workspace_projects) show the new shape, workspace_repos
  is gone, and ls {DataDir}/repos/ shows renamed directories.
• /projects → Add repo → walk through token/account/repo/branch
  → submit → new project appears, clone+index runs to completion.
• Open the project detail page → use Add to workspace to link
  it into a workspace.
• Open the workspace → see the project in its list (rendered as a
  Project row, not a RepoCard) with status badge; Unlink
  removes it from the workspace but /projects still shows it.
• Workspace search returns hits from the linked project.
• Delete the project from /projects/{hash} → workspaces' lists
  update, git_repos row is gone, the same upstream can be re-added.
• Re-register the GitHub webhook URL to the new
  /api/v1/webhooks/github/{path_hash} route, push a commit → the
  clone_repo job fires.

🤖 Generated with Claude Code