feat(lfx): add lfx[bundles] extra and keep lfx engine-only (#13565)

* feat(bundles): add lfx-bundles metapackage skeleton

Creates the manifest-less lfx-bundles distribution (the langchain-community
model) that the long-tail providers will move into. Empty skeleton for now;
the bulk move (scripts/migrate/consolidate_bundles.py) populates the provider
folders + per-provider extras later.

- src/bundles/lfx-bundles: a single pyproject declaring the lfx.bundles
  entry-point (lfx_bundles = "lfx_bundles"), an lfx>=1.10.0,<2.0.0 pin, and a
  generated (currently empty) `all` extra; plus a bare lfx_bundles namespace
  package and a README documenting the model + install stories
- wired into the root workspace via the existing bundle marker blocks:
  dep lfx-bundles[all]>=1.0,<2.0, uv source, and member
- hyphen dir name so release.yml's src/bundles/*/pyproject.toml glob builds
  it with zero workflow change

Verified: the wheel builds (entry_points.txt carries the lfx.bundles group);
load_lfx_bundles_extensions (PR-1) discovers the entry point and the empty
skeleton registers zero providers with no error.

* feat(lfx): add lfx[bundles] extra and keep lfx engine-only

lfx ships no bundles by default. The new optional extra pulls the long-tail
metapackage for users who want the provider components without the full
langflow server install.

- src/lfx/pyproject.toml: [project.optional-dependencies]
  bundles = ["lfx-bundles[all]>=1.0,<2.0"]; intentionally NO lfx[all]
- pip install lfx          -> engine only
  pip install "lfx[bundles]" -> engine + the lfx-bundles long tail
  (documented as a headless/serverless deployment footnote, not a headline)

Verified against the built lfx wheel METADATA: lfx-bundles appears only under
`extra == "bundles"`, never in core Requires-Dist, so the engine-only default
is preserved.

* fix(ci): nightly bundle rename follows [extras] refs and self-refs

Two gaps in update_bundle_versions.py around extras suffixes, both fatal
or silently wrong for the first nightly carrying the lfx-bundles
metapackage:

- update_root_pyproject_for_bundle's dep regex required the version
  specifier immediately after the name, so "lfx-bundles[all]>=1.0,<2.0"
  (a MAIN dep) was left unrewritten while the workspace member was
  renamed to lfx-bundles-nightly; uv lock then tries to resolve stable
  lfx-bundles from PyPI, where it does not exist. The same gap silently
  left "lfx-docling[local]>=0.1.0" optional-dep refs pointing at the
  stable distribution. The regex now tolerates an [extras] group and
  carries it into the replacement.

- rename_bundle_pyproject skipped self-referencing extras, so the
  metapackage's generated `all` extra kept 45 "lfx-bundles[<provider>]"
  members after the rename, pulling the stable distribution (same
  lfx_bundles import package, install collision) once published. Self
  refs now follow the rename, idempotently.

Tests drive the real script module, mirroring test_bundle_lfx_pin.py.
This closes the PR-2 audit item flagged when the metapackage was
introduced. The canonical-pre-release cutover would retire the nightly
rename entirely; until it lands, the rename must be correct.

Author: erichare

src/lfx/pyproject.toml

@@ -53,6 +53,18 @@ dependencies = [
     "OpenDsStar==1.0.26; python_version >= '3.11' and python_version < '3.14' and (sys_platform != 'darwin' or platform_machine != 'x86_64')",
 ]
 
+[project.optional-dependencies]
+# Engine-only by default: ``pip install lfx`` ships NO bundles.  This optional
+# extra pulls the long-tail metapackage for users who want the provider
+# components without the full ``langflow`` server install:
+#
+#   pip install lfx              -> engine only
+#   pip install "lfx[bundles]"   -> engine + the lfx-bundles long tail
+#
+# Documented as a headless/serverless deployment footnote, not a
+# getting-started headline.  There is intentionally NO ``lfx[all]``.
+bundles = ["lfx-bundles[all]>=1.0,<2.0"]
+
 [project.scripts]
 lfx = "lfx.__main__:main"
 lfx-mcp = "lfx.mcp.__main__:main"