Hardened GitHub Actions runners block direct access to public registries.
This adds OIDC-based authentication to JFrog Artifactory and routes all
uv package downloads through the db-pypi proxy. A `make fix-lockfile`
target prevents proxy URLs from leaking into the committed lockfile.

The JFrog proxy URL structure has /packages/packages/ (the proxy path
plus the original PyPI path), so the sed replacement must map
db-pypi/packages to files.pythonhosted.org (without /packages suffix).

Also, uv lock through JFrog drops size/upload-time metadata from the
lockfile. Restore committed lockfiles with git checkout before the diff
check so only formatting changes and accidentally committed proxy URLs
are caught.

The tagging workflow used setup-uv v4.2.0 without a version pin,
installing whatever uv release was latest. Align it with the rest
of the workflows: setup-uv v7.3.0 pinned to uv 0.6.5.

Release workflows need special publish runners and coordination with the
security team per the migration guide. Keep this PR focused on unblocking
CI (tests, fmt, check-manifest).

Remove uv lock from CI and use uv sync --frozen instead of --locked.
If the hardened runners transparently route files.pythonhosted.org
through the JFrog proxy, downloads from lockfile URLs should work
without rewriting them.

uv run without --frozen triggers auto-sync, which re-locks the lockfile
with JFrog URLs and drops size/upload-time metadata. Pass --frozen to
all uv run calls since we already synced the environment explicitly.

Add UV_SYNC_FLAGS and UV_RUN_FLAGS variables to the Makefile so CI can
pass --frozen without duplicating commands. Local dev defaults remain
unchanged (--locked for sync, no flags for run).

Set UV_FROZEN=1 in the composite action so uv natively skips lockfile
re-resolution on all commands. This lets workflows call make dev test
and make dev fmt unchanged -- no Makefile modifications needed beyond
the new fix-lockfile target.

Replace the manual OIDC token exchange (~20 lines of curl/jq) with the
jfrog/setup-jfrog-cli action, which handles OIDC internally and exposes
the token via step outputs. Same action + SHA as the CLI repo (PR #4875).

uv rejects --locked and --frozen together. Add UV_LOCK_FLAG variable
(defaults to --locked) that the composite action clears via env var,
letting UV_FROZEN=1 handle lockfile behavior in CI instead.

Run uv lock after JFrog setup to rewrite the lockfile with JFrog URLs
(same versions, different registry). This lets make dev test and make
dev fmt work unchanged with --locked. In fmt, restore committed
lockfiles before the diff check so only formatting issues and
accidentally committed proxy URLs are caught.