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.

.github/dependabot.yml

@@ -29,6 +29,14 @@ updates:
       - "/libs/langchain_v1/"
     schedule:
       interval: "monthly"
+    versioning-strategy: increase
+    ignore:
+      - dependency-name: "langchain-core"
+      - dependency-name: "langchain"
+      - dependency-name: "langchain-classic"
+      - dependency-name: "langchain-text-splitters"
+      - dependency-name: "langchain-tests"
+      - dependency-name: "langchain-model-profiles"
     groups:
       minor-and-patch:
         patterns:
@@ -61,6 +69,14 @@ updates:
       - "/libs/partners/xai/"
     schedule:
       interval: "monthly"
+    versioning-strategy: increase
+    ignore:
+      - dependency-name: "langchain-core"
+      - dependency-name: "langchain"
+      - dependency-name: "langchain-classic"
+      - dependency-name: "langchain-text-splitters"
+      - dependency-name: "langchain-tests"
+      - dependency-name: "langchain-model-profiles"
     groups:
       minor-and-patch:
         patterns:
@@ -81,6 +97,14 @@ updates:
       - "/libs/model-profiles/"
     schedule:
       interval: "monthly"
+    versioning-strategy: increase
+    ignore:
+      - dependency-name: "langchain-core"
+      - dependency-name: "langchain"
+      - dependency-name: "langchain-classic"
+      - dependency-name: "langchain-text-splitters"
+      - dependency-name: "langchain-tests"
+      - dependency-name: "langchain-model-profiles"
     groups:
       minor-and-patch:
         patterns: