ci: add InTx linter replacing ruleguard rule (#24422)

Replace the old `InTx` ruleguard rule in `scripts/rules.go` with a
custom in-tree `go/analysis` analyzer under `scripts/intxcheck/`. The
new analyzer catches the same direct and pass-through misuse classes as
before, plus two new classes the pattern-matcher couldn't reach:

- **Indirect same-package helper misuse** — flags `p.someHelper(ctx)`
inside `InTx` when the helper body uses the outer store (the PR #24369
bug class).
- **Nested dangerous closures** — descends into `go func() { ... }()`,
`defer func() { ... }()`, and immediately-invoked function literals.

The analyzer uses semantic `types.Object` identity instead of raw
expression string comparison, which avoids false positives from
closure-local shadowing and catches simple aliases like `outer := s.db`
and `alias := s`.

This PR also fixes three real outer-store-inside-transaction bugs the
new analyzer surfaced:

- `coderd/wsbuilder/wsbuilder.go`: `FindMatchingPresetID` and
`getWorkspaceTask` now use the inner transaction store instead of
`b.store`.
- `enterprise/dbcrypt/dbcrypt.go`: `ensureEncrypted` now calls
`s.InsertDBCryptKey` (the tx-wrapped store) instead of
`db.InsertDBCryptKey`. The `dbCrypt.InTx` method wraps the raw tx in a
new `*dbCrypt`, so `s.InsertDBCryptKey` still dispatches through the
encryption layer.

Two call sites need `// intxcheck:ignore` suppressions. Both are one-off
patterns that only look like misuse because the analyzer doesn't track
assignments — proving them safe would require full dataflow analysis,
which is well beyond what a targeted lint like this should attempt:

- `coderd/database/dbfake/dbfake.go` — `b.db` is reassigned to `tx` on
the preceding line, so `b.doInTX()` actually uses the transaction. The
analyzer sees the original `b.db` identity and flags it.
- `coderd/database/db_test.go` — test intentionally passes the outer
store to `require.Equal` to assert that nested `InTx` returns the same
handle.

Suppressions use `// intxcheck:ignore` instead of `//nolint:intxcheck`
because `intxcheck` runs as a standalone `go/analysis` tool outside
golangci-lint. golangci-lint's `nolintlint` checker flags `//nolint`
directives for linters it doesn't control, so we use a custom comment
prefix to avoid that conflict.

coderd/wsbuilder/wsbuilder.go

@@ -490,7 +490,7 @@ func (b *Builder) buildTx(authFunc func(action policy.Action, object rbac.Object
 		}
 
 		if b.templateVersionPresetID == uuid.Nil {
-			presetID, err := prebuilds.FindMatchingPresetID(b.ctx, b.store, templateVersionID, names, values)
+			presetID, err := prebuilds.FindMatchingPresetID(b.ctx, store, templateVersionID, names, values)
 			if err != nil {
 				return BuildError{http.StatusInternalServerError, "find matching preset", err}
 			}
@@ -528,7 +528,7 @@ func (b *Builder) buildTx(authFunc func(action policy.Action, object rbac.Object
 			return BuildError{code, "insert workspace build", err}
 		}
 
-		task, err := b.getWorkspaceTask()
+		task, err := b.getWorkspaceTask(store)
 		if err != nil {
 			return BuildError{http.StatusInternalServerError, "get task by workspace id", err}
 		}
@@ -677,11 +677,11 @@ func (b *Builder) getTemplateVersionID() (uuid.UUID, error) {
 
 // getWorkspaceTask returns the task associated with the workspace, if any.
 // If no task exists, it returns (nil, nil).
-func (b *Builder) getWorkspaceTask() (*database.Task, error) {
+func (b *Builder) getWorkspaceTask(store database.Store) (*database.Task, error) {
 	if b.hasTask != nil {
 		return b.task, nil
 	}
-	t, err := b.store.GetTaskByWorkspaceID(b.ctx, b.workspace.ID)
+	t, err := store.GetTaskByWorkspaceID(b.ctx, b.workspace.ID)
 	if err != nil {
 		if xerrors.Is(err, sql.ErrNoRows) {
 			b.hasTask = ptr.Ref(false)
@@ -1382,7 +1382,7 @@ func (b *Builder) checkUsage() error {
 		return BuildError{http.StatusInternalServerError, "Failed to fetch template version", err}
 	}
 
-	task, err := b.getWorkspaceTask()
+	task, err := b.getWorkspaceTask(b.store)
 	if err != nil {
 		return BuildError{http.StatusInternalServerError, "Failed to fetch workspace task", err}
 	}