Task: Add the release installer and the Installing section

TASK-DESCRIPTION

Create: prompts/features/07-release-installer.md
Modify: prompts/features/00-features.md
Modify: scripts/install.sh
Modify: scripts/release-package.sh
Modify: tests/11-release-install.sh
Modify: README.md
Modify: prompts/tasks/00-tasks.md
Modify: TODO.md

The release installer follows the AppImage project: one command fetches the release tarball for this machine, verifies it against SHA256SUMS, installs it into $PREFIX, and then registers the vCard handler. It supports a pinned VERSION, a local VCARD_INTEGRATION_TARBALL, the VCARD_INTEGRATION_SKIP_VERIFY override, a source-archive build when no prebuilt asset matches the machine, and VCARD_INTEGRATION_NO_HANDLER=1 to skip the registration.

README.md gains an Installing section with the one-line command, the PREFIX and VERSION controls, the handler step and its reversal, the make install path for a checkout, and make release-publish. The generated release notes describe the same behavior.

TASK-OUTPUT

Produce these complete files in this order, then the VERIFICATION: line: 1. prompts/features/07-release-installer.md 2. prompts/features/00-features.md 3. scripts/install.sh 4. scripts/release-package.sh 5. tests/11-release-install.sh 6. README.md 7. prompts/tasks/00-tasks.md 8. TODO.md

TASK-CONTEXT

The reference is gnome-appimage-integration/README.md and its scripts/install.sh. This project’s handler is registered with vcard-integrate handler install and reversed with vcard-integrate handler uninstall. A handler failure during the release install is reported rather than fatal, because the tools are installed either way; make install is the path that fails closed.

The installer must verify the download and must not prompt. The handler step must be skippable and reversible.

TASK-FILES

Operation	Path
create	`prompts/features/07-release-installer.md`
modify	`prompts/features/00-features.md`
modify	`scripts/install.sh`
modify	`scripts/release-package.sh`
modify	`tests/11-release-install.sh`
modify	`README.md`
modify	`prompts/tasks/00-tasks.md`
modify	`TODO.md`

TASK-VERIFY

Run: make test from the repository root.
Expected: exit status 0, with 11-release-install reporting ok for the local, HTTP, handler, and opt-out cases.
Run: VERSION=v0.1.0 PREFIX=/tmp/vcard-prefix HOME=/tmp/vcard-home XDG_DATA_HOME=/tmp/vcard-home/.local/share XDG_CONFIG_HOME=/tmp/vcard-home/.config sh scripts/install.sh.
Expected: the download matches its digest, the programs install, and handler status reports both types with vcard-handler.desktop.

TASK-FEATURES

prompts/features/07-release-installer.md

TASK-ACCEPTANCE

RELEASE-INSTALLER-R001
RELEASE-INSTALLER-R002
RELEASE-INSTALLER-R003
RELEASE-INSTALLER-R004
RELEASE-INSTALLER-R005
RELEASE-INSTALLER-R006
RELEASE-INSTALLER-R007
RELEASE-INSTALLER-R008

OUTPUT: the complete files in the order listed, ending with the VERIFICATION: line.