release v0.15.0

- **`agent-shape.toml` at repo root.** 20-subcommand adoption stub for the
  jig methodology, cross-validated via `jig check --binary` so the
  manifest stays consistent with the actual CLI surface.
- **`scripts/agent-shape-fixture.sh`.** Idempotent fixture builder that
  sets up three git registries (one writable, two readonly mirrors) plus
  a project containing six items spanning current, drifted,
  registry-missing, and upstream-advanced states. Used as the harness
  for agent-shape baselining.
- **5 tuning tasks** under the agent-shape work, exercising the fixture
  states above.
- **Treatment v0 discoverability aliases.** `rune registry list` now has
  a parent `registry` command with a `ls` alias, `rune config list`
  picks up an `ls` alias, and `rune add --registry` is exposed as a
  visible alias for `--from`. Targets the most common path drift the
  agent-shape baseline surfaced.
- **`hero.svg` and `avatar.svg`** in the nomograph paper-palette OV-1
  grammar, plus a `CODEOWNERS` file.

- **`skill_path` is now layout-aware.** It falls back from the typed
  subdirectory layout (`skills/<name>`) to the legacy flat layout
  (`<name>` at registry root) the same way `artifact_path` already did.
  Without this fix, `rune upstream` could not find imported skills in
  writable registries that used the typed-subdirectory layout. Includes
  a `skill_path_typed_vs_legacy` regression test covering both layouts
  plus the directory-skill case.