Bump to 0.6.6 — release-flow docs + when-to-bump policy

Ships the new RELEASE.md to Hex (and therefore hexdocs.pm) so the
release process — including the bump rules added in this release
(doc-only improvements warrant a bump because hexdocs is built from
the published version; tests-and-docs are non-negotiable for new
functionality) — is visible to anyone reading from outside the repo,
not just contributors with a local clone.

Also adds the .githooks/ scaffolding and the CLAUDE.md "Release
flow" section that points to RELEASE.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ci: per-step idempotency so re-runs back-fill missing pieces

Previously the workflow had one all-or-nothing tag-exists check: if the
tag was already there (e.g. pushed manually before this workflow
existed), every later step was skipped — including the Hex publish.
That stranded mob_dev 0.5.4 and mob_new 0.3.2: tagged + released on
GitHub, never shipped to Hex.

Now each step checks its own precondition:
- Tag: git rev-parse refs/tags/<v>
- GitHub Release: gh release view <v>
- Hex publish: mix hex.info <pkg> <v> | grep Config:

So `workflow_dispatch` re-runs do exactly what's missing and no more.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Merge pull request #2 from leonardb/patch-1

Fix device_capabilities.md to remove spurious triple back-ticks

credo

Updated plan