chore: add release-please for automated release management (#25)

Adds release-please (Google, v4 GitHub Action) configuration per
ADR-0015 release standardization. Creates Release PRs automatically
on push to main, with VERSION file as single source of truth.

Cargo.toml version managed natively by release-type: rust.
Existing release.yml workflow is unchanged -- release-please creates
the tags that trigger it.

Co-authored-by: Claude <noreply@anthropic.com>

Author: HerbHall

.github/workflows/release-please.yml

@@ -0,0 +1,22 @@
+name: Release Please
+
+on:
+  push:
+    branches: [main]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    outputs:
+      release_created: ${{ steps.release.outputs.release_created }}
+      tag_name: ${{ steps.release.outputs.tag_name }}
+      version: ${{ steps.release.outputs.version }}
+    steps:
+      - uses: googleapis/release-please-action@v4
+        id: release
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}

.release-please-manifest.json

@@ -0,0 +1,3 @@
+{
+  ".": "0.7.0"
+}

VERSION

@@ -0,0 +1 @@
+0.7.0

release-please-config.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
+  "packages": {
+    ".": {
+      "release-type": "rust",
+      "version-file": "VERSION",
+      "changelog-path": "CHANGELOG.md",
+      "bump-minor-pre-major": true,
+      "bump-patch-for-minor-pre-major": true
+    }
+  },
+  "changelog-sections": [
+    { "type": "feat", "section": "Features" },
+    { "type": "fix", "section": "Bug Fixes" },
+    { "type": "perf", "section": "Performance" },
+    { "type": "refactor", "section": "Code Refactoring", "hidden": true },
+    { "type": "docs", "section": "Documentation", "hidden": true },
+    { "type": "chore", "section": "Miscellaneous", "hidden": true },
+    { "type": "test", "section": "Tests", "hidden": true }
+  ]
+}