ci(infra): harden Dependabot version-bound preservation (#37510)

Dependabot has been stripping upper/lower bounds from internal
`langchain-*` deps in partner `pyproject.toml` files (e.g. #37288
reduced `langchain-core>=1.3.2,<2.0.0` to bare `langchain-core`). Locks
down the config so bumps preserve existing specifiers, and restores the
bounds it already mangled across the monorepo.

## Changes
- Add `versioning-strategy: increase` to every `uv` ecosystem block in
`.github/dependabot.yml` so future bumps move the lower bound in place
instead of rewriting the constraint.
- Ignore workspace-internal packages (`langchain-core`, `langchain`,
`langchain-classic`, `langchain-text-splitters`, `langchain-tests`,
`langchain-model-profiles`) on every `uv` block — these are editable
installs from local paths and their published constraints are
hand-curated for release, not Dependabot's to bump.
- Restore stripped bounds across all `libs/` packages — runtime
`dependencies` and every dep group (`test`, `dev`, `test_integration`,
`typing`, `lint`) — to `>=1.4.0,<2.0.0` for `langchain-core` and
`>=1.0.0,<2.0.0` for the other internal packages.

libs/langchain_v1/pyproject.toml

@@ -72,7 +72,7 @@ test = [
     "syrupy>=5.0.0,<6.0.0",
     "toml>=0.10.2,<1.0.0",
     "blockbuster>=1.5.26,<1.6.0",
-    "langchain-tests",
+    "langchain-tests>=1.0.0,<2.0.0",
     "langchain-openai",
 ]
 lint = [
@@ -88,8 +88,8 @@ test_integration = [
     "wrapt>=1.15.0,<3.0.0",
     "python-dotenv>=1.0.0,<2.0.0",
     "langchainhub>=0.1.16,<1.0.0",
-    "langchain-core",
-    "langchain-text-splitters",
+    "langchain-core>=1.4.0,<2.0.0",
+    "langchain-text-splitters>=1.0.0,<2.0.0",
 ]
 
 [tool.uv]