ci: add renovate and auto-approver config, drop dependabot

Author: pkarolyi

.auto-approve.yaml

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+paths:
+  - path: "*.md"
+    reason: "Documentation"
+  - path: "/catalog-info.yaml"
+    reason: "Backstage metadata"
+  - path: "**/.claude/**"
+    reason: "Claude Code configuration and skills, not library code"
+  - path: "/renovate.json5"
+    reason: "Renovate configuration"

.gitar/config/approve.md

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+# Auto-approval rules
+
+This file defines rules Gitar should use to auto-approve merge requests in this
+repository. Each rule has a natural-language `When` condition and an `Action`.
+
+Dependency updates are out of scope here. Renovate labels its non-major dev
+dependency MRs `automerge`, and a bot approves and merges them. Updates to
+runtime dependencies change what users of the published package install, so
+they always wait for a human. Do not auto-approve dependency update MRs.
+
+## Rule: Documentation-only changes
+
+**When:** Every changed file in the merge request is a Markdown file (`.md`) or
+`catalog-info.yaml`, and the merge request does not touch source code, CI
+configuration, or dependency manifests.
+
+**Action:** Approve the merge request automatically and add the label
+`auto-approved`.
+
+## Rule: Test-only changes
+
+**When:** Every changed file in the merge request is under `deepl-java/src/test/`, and
+the merge request does not modify library source code, CI configuration, or
+dependency manifests.
+
+**Action:** Approve the merge request automatically and add the label
+`auto-approved`.
+
+## Rule: Re-approve after rebase
+
+**When:** The merge request was previously approved by at least one human
+reviewer, and the approval was reset solely because the author rebased or
+force-pushed. The substantive diff relative to the target branch is identical
+to the version that received the original approval, and no new commits with new
+logic or content were added since that approval.
+
+**Action:** Approve the merge request automatically and add the label
+`auto-approved`.
+
+## Rule: Safe, backwards-compatible change
+
+**When:** All of the following hold for the merge request:
+
+- **CI is green.** The pipeline for the latest commit has completed
+  successfully, with no failing, running, or pending required jobs.
+- **Tests cover the change if needed.** New or changed library behavior has a
+  matching case under `deepl-java/src/test/`. Changes that genuinely need no tests, such
+  as comments or log text, may omit them.
+- **The diff matches the MR description.** The code changes do exactly what the
+  title and description say, with no unexplained or unrelated changes bundled
+  in.
+- **The public API stays backwards compatible.** Adding new capability is fine:
+  new methods, new classes, new optional parameters, new options, or new
+  response fields passed through to callers. What is not allowed is breaking
+  what already exists. Do not auto-approve a removed or renamed public class,
+  method, parameter, constant, or error type, a behavior change in an existing
+  method, a raised minimum supported Java version, or a change to the runtime dependencies in
+  `deepl-java/build.gradle.kts`. This library is published to Maven Central as `com.deepl.api:deepl-java`, so a break here
+  lands in user code with the next release.
+
+**Action:** Approve the merge request automatically and add the label
+`auto-approved`.
+
+> Apply this rule strictly: only approve when the merge request **clearly and
+> unambiguously** satisfies every condition above. If any condition is
+> uncertain, leave the merge request for human review.
+
+## Rule: Everything else
+
+**When:** The merge request does not clearly satisfy one of the rules above.
+This includes CI configuration (`.gitlab-ci.yml`, `.github/`),
+`.auto-approve.yaml`, `.gitar/**`, `renovate.json5`, and a release cut, which
+updates the version numbers in the files that `.bumpversion.toml` lists and
+moves the `[Unreleased]` section of `CHANGELOG.md`.
+
+**Action:** Do not auto-approve. Leave the merge request for human review.

.github/dependabot.yml

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+// Renovate configuration for the GitLab repository where this library is
+// developed. Dependency updates do not run on the GitHub mirror, so users of
+// the library can ignore this file.
+{
+  $schema: "https://docs.renovatebot.com/renovate-schema.json",
+  extends: [
+    "local>deepl-org/deepl/backend/oss-client-libs/ci-libs-for-client-libraries:renovate-client-libraries.json5",
+  ],
+}