fix(coderd): filter build instance agents in SQL (#25031)

Replaces the per-agent Go-side template-version filter in
`handleAuthInstanceID` with a purpose-built SQL query.

`GetWorkspaceBuildAgentsByInstanceID` joins `workspace_agents ->
workspace_resources -> workspace_builds -> provisioner_jobs ->
workspaces` and excludes:

- non-`workspace_build` provisioner jobs (template-version-import,
dry-run)
- deleted agents and sub-agents
- deleted workspaces

The handler:

- drops the per-candidate `GetWorkspaceResourceByID` /
`GetProvisionerJobByID` lookups
- drops the `provisioner_jobs.input` JSON parsing and the follow-up
`GetWorkspaceBuildByID` call
- compares `latestHistory.ID` against `selected.WorkspaceBuildID`
returned directly from the query
- preserves the existing recycled-instance safety check and matching
response codes

One intentional behavior tightening: agents whose workspace is deleted
now return 404 (previously they could reach the recycled-instance check
and return 400, or 200 if the stale build was still latest). This
matches the existing token-auth path, which already refuses to
authenticate against deleted workspaces.

The original `GetWorkspaceAgentsByInstanceID` query is intentionally
untouched. It remains the generic raw lookup used elsewhere in tests and
helpers.

The dbauthz wrapper for the new query uses the system-read fast path
with `fetchWithPostFilter` for non-system reads, with `RBACObject()`
delegating to the embedded `WorkspaceTable`.

Tests:

- new `TestGetWorkspaceBuildAgentsByInstanceID` covering newest-first
ordering, exclusion of deleted/sub agents, exclusion of template-import
and dry-run jobs, and exclusion of deleted workspaces
- new dbauthz mock test for `GetWorkspaceBuildAgentsByInstanceID`
- new `TestPostWorkspaceAuthAWSInstanceIdentity/RecycledInstanceID`
exercising the recycled-instance rejection branch (HTTP 400 when the
agent's build is no longer latest)
- existing `TestPostWorkspaceAuth{AWS,Azure,Google}InstanceIdentity`
continue to cover the handler end to end (including the template-version
+ workspace-build same-instance-ID scenario via
`setupInstanceIDWorkspace`)

> Mux is acting on Mike's behalf.

coderd/database/modelmethods.go

@@ -932,6 +932,11 @@ func (r GetWorkspaceAgentAndWorkspaceByIDRow) RBACObject() rbac.Object {
 	return r.WorkspaceTable.RBACObject()
 }
 
+// A workspace agent belongs to the owner of the associated workspace.
+func (r GetWorkspaceBuildAgentsByInstanceIDRow) RBACObject() rbac.Object {
+	return r.WorkspaceTable.RBACObject()
+}
+
 // UpsertConnectionLogParams contains the parameters for upserting a
 // connection log entry. This struct is hand-maintained (not generated
 // by sqlc) because the single-row UpsertConnectionLog query was