bug(release): auto-generated release notes use wrong comparison range

[MAfarrag]

Context

The actions/release/github composite action creates GitHub releases via
softprops/action-gh-release@v2 with generate_release_notes: true.
The auto-generated notes compare against the wrong previous tag, including
PRs from prior releases.

Example: Release 0.10.0
shows all PRs since 0.8.0 instead of only changes since 0.9.1.
The release notes list 14 PRs when only 3 belong to this release (#170, #172, #175).

Problem / Current Behaviour

- uses: softprops/action-gh-release@v2
  with:
    generate_release_notes: true

softprops/action-gh-release calls the GitHub Releases API which auto-detects
the "previous release" to compare against. GitHub picked 0.8.0 instead of
0.9.1, producing a comparison range of 0.8.0...0.10.0 that includes PRs
already released in 0.9.0 and 0.9.1.

The softprops/action-gh-release action does not expose a previous_tag
input, so there's no way to control which tag GitHub compares against.

Affected locations

File	Symbol	Notes
actions/release/github/action.yml	Publish GitHub Release step	generate_release_notes: true

Proposed Solution

Replace generate_release_notes: true with an explicit body extracted
from the commitizen-generated changelog file. Since commitizen already
generates accurate, scoped release notes during cz bump, we should use
those instead of GitHub's auto-generated notes.

- name: Extract changelog for current release
  id: changelog
  shell: bash
  run: |
    VERSION="${{ steps.bump_version.outputs.NEW_VERSION }}"
    # Extract the section for this version from the changelog
    BODY=$(awk "/^## ${VERSION}/,/^## [0-9]/" "$CHANGELOG_FILE" \
           | head -n -1)
    echo "body<<CHANGELOG_EOF" >> $GITHUB_OUTPUT
    echo "$BODY" >> $GITHUB_OUTPUT
    echo "CHANGELOG_EOF" >> $GITHUB_OUTPUT

- uses: softprops/action-gh-release@v2
  with:
    body: ${{ steps.changelog.outputs.body }}
    generate_release_notes: false

Alternatively, use gh api directly with the previous_tag_name parameter
which the GitHub Releases API supports but softprops/action-gh-release
does not expose.

Out of Scope

• Fixing existing broken release notes (can be manually edited)
• Changing commitizen's changelog format

Effort Estimate

Size: S
Rationale: replace one step + add changelog extraction step

Definition of Done

• Release notes only contain changes since the previous release
• Notes sourced from commitizen changelog (single source of truth)
• Tested with a patch release to verify correct scoping