build(etl): rename submodule path to match directory for Go consumability

[raymondjacobson]

Summary

The etl submodule declared its module path as `github.com/OpenAudio/go-openaudio/etl` while living in the directory `pkg/etl/`. Go's multi-module repo rules require the module path to match the directory path within the repo — otherwise external consumers can't resolve the submodule at all, regardless of how tags are formatted.

Quoting Go's docs on multi-module repos:

A version tag in a module subdirectory must be prefixed with the relative path from the root of the repository to the module's go.mod file, followed by '/'. For example, the module example.com/repo/sub at version v1.5.2 corresponds to the tag sub/v1.5.2.

Concretely, with the old setup:

```
$ go get github.com/OpenAudio/go-openaudio/etl@v1.3.0
go: module github.com/OpenAudio/go-openaudio@v1.3.0 found,
but does not contain package github.com/OpenAudio/go-openaudio/etl
```

Go interprets the path as a subpackage of the parent module (since no `etl/` directory exists at repo root) and never finds it. The pkg/etl/v1.3.0 tag I pushed earlier in this thread is currently inert.

Changes

File	Change
`pkg/etl/go.mod`	`module github.com/OpenAudio/go-openaudio/etl` → `.../pkg/etl`
`go.mod` (root)	require + replace directive bumped to new module path
54 `.go` files	mechanical import-path rewrite via sed
`release-please-config.json`	`pkg/etl` package's `component` and `package-name` changed from `"etl"` → `"pkg/etl"` so generated tags are `pkg/etl/vX.Y.Z`
`pkg/etl/README.md`, `pkg/etl/FEATURE.md`	stale path references

After this lands

1. The previously-pushed `pkg/etl/v1.3.0` tag becomes externally consumable: `go get github.com/OpenAudio/go-openaudio/pkg/etl@v1.3.0` resolves.
2. Release-please will open a new release PR; its first lockstep cut will produce `v1.4.0` + `pkg/etl/v1.4.0` tags (correct Go submodule tag format).
3. The deleted `etl/v1.3.0` tag stays gone — release-please won't recreate that format.

Side note

Closed #298 (the release-please PR with the old `etl/v1.4.0` tag format) before opening this. Release-please will reopen with the correct format after this merges.

Verified

`go build ./...` clean in both modules. Only `go vet ./...` warnings are pre-existing in unrelated packages.

[raymondjacobson]

Updated to also fix the 10 .templ source files in pkg/explorer/templates/pages/ — they still had the old github.com/OpenAudio/go-openaudio/etl/db import. Without this fix, running templ generate after merge would regenerate the *_templ.go files with the broken old import path and break the build.

To answer the original question: yes, the explorer keeps working in prod after this change. Confirmed by:

• go build ./pkg/explorer/... clean (explorer compiles)
• go build ./cmd/openaudio/... clean (the prod binary that embeds explorer compiles)
• All 10 explorer page .templ sources have the corrected import; the generated *_templ.go files (touched by the original sed) match. Future templ generate runs stay consistent.

The explorer imports (pkg/etl, pkg/etl/db, pkg/etlserver) all resolve via the in-repo replace directive in the root go.mod, which I updated to the new path. Production builds from the repo itself, so consumption mechanics are identical to today — the rename only affects external Go-module consumers.

Updated PR is force-pushed; please re-review.