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/partners/deepseek/pyproject.toml

@@ -23,7 +23,7 @@ classifiers = [
 version = "1.1.0"
 requires-python = ">=3.10.0,<4.0.0"
 dependencies = [
-    "langchain-core",
+    "langchain-core>=1.4.0,<2.0.0",
     "langchain-openai>=1.1.0,<2.0.0",
 ]
 
@@ -45,7 +45,7 @@ test = [
     "pytest-watcher>=0.3.4,<1.0.0",
     "pytest-timeout>=2.3.1,<3.0.0",
     "pytest-xdist>=3.6.1,<4.0.0",
-    "langchain-tests",
+    "langchain-tests>=1.0.0,<2.0.0",
     "langchain-openai",
 ]
 test_integration = []