v0.112.0

Embeds ezbake functionality into kiln as a carvel subcommand

Embeds ezbake functionality into kiln as a Go library, adding full
lifecycle support for baking, uploading, publishing, and reproducibly
re-baking Carvel/Kubernetes tiles.

### New commands

- **`kiln carvel bake`** — Transforms an imgpkg bundle into a BOSH
release and bakes it into a `.pivotal` file. When a `Kilnfile.lock` is
present, downloads the cached BOSH release from Artifactory instead of
regenerating locally.
- **`kiln carvel upload`** — Generates a BOSH release from Carvel tile
source, uploads the tarball to Artifactory, and writes `Kilnfile.lock`
with the remote location and checksum.
- **`kiln carvel publish`** — Bakes a final tile with version stamping
and produces a JSON bake record for reproducible builds.
- **`kiln carvel re-bake`** — Reproduces a tile build from a bake
record, verifying source revision matches the git checkout.

### New packages

- **`internal/carvel`** — Core `Baker` that reads tile metadata
(`base.yml`) and imgpkg bundles, generates a BOSH release via `bosh
create-release`, creates a kiln-compatible structure in `.ezbake/`, and
invokes `kiln bake` to produce the final `.pivotal` file.
- **`internal/carvel/models`** — Data models for tile metadata, Carvel
lockfiles, package installs, runtime configs, and jobs.

### Architecture

The `kiln carvel` command group is registered in `main.go` and delegates
to subcommands via `jhanda.CommandSet`. Each subcommand uses the
standard `flags.Standard` embedded struct to load Kilnfiles with
variable interpolation (e.g., from `~/.kiln/credentials.yml`), keeping
credential handling consistent with existing kiln commands. The `Baker`
interface drives the imgpkg-to-BOSH transformation and tile assembly.

### Other changes

- **Consistent lockfile serialization** — `CarvelLockfile` now uses
`releases` (plural, as a slice) instead of `release` (singular),
matching the standard `KilnfileLock` format in `pkg/cargo`.
- **CI lint fixes** — Resolved all `staticcheck` and `unused` findings
across the new files (capitalized error strings, redundant embedded
field selectors, unnecessary `fmt.Sprintf`, unused functions).
- **CI test stability** — Test `BeforeEach` blocks that run `git commit`
now pass `-c user.name` / `-c user.email` inline so they work on CI
runners without global git config.
- **Acceptance and unit tests** — Full test coverage for all four
subcommands, the `Baker`, and the Carvel model types.

## Usage

```sh
# Bake a Carvel tile locally
kiln carvel bake --source-directory /path/to/tile --output-file tile.pivotal

# Upload the BOSH release to Artifactory (writes Kilnfile.lock)
kiln carvel upload --source-directory /path/to/tile --kilnfile /path/to/Kilnfile

# Publish a versioned tile and produce a bake record
kiln carvel publish --source-directory /path/to/tile --output-file tile.pivotal --version 1.0.0 --final

# Reproduce a tile from a bake record
kiln carvel re-bake --output-file tile.pivotal bake-record.json
```

## Test plan

- [x] `go test ./internal/carvel/...` — Baker and model unit tests
- [x] `go test ./internal/commands/...` — All carvel subcommand tests
(bake, upload, publish, re-bake)
- [x] `go test ./internal/acceptance/carvel/...` —
Integration/acceptance tests
- [x] `golangci-lint run ./...` — Zero lint issues