refactor: simplify installer primitives and clarify runtime plan

[acburdine]

Simplifies the S1/S2 installer foundations while retaining the configuration, routing and recovery interfaces needed by the Ghost-CLI replacement plan. Stacked on #283.

• Require curl for bounded HTTP/HTTPS probes and use Compose readiness instead of custom HTTP and health-polling code. HTTPS now probes the published host port with Host/SNI preserved; it remains a routing check that accepts internal certificates.
• Pull Ghost once and persist GHOST_IMAGE_REF=ghost@sha256:... for both Ghost and Tinybird sync. Fail when a digest is unavailable. Changing the recorded request tag alone no longer changes the installed image.
• Generate fresh .env configuration in one atomic write and use existing jq numeric sorting for stable/beta release discovery, independent of Git sorting configuration.
• Resolve the plan's conflicting JSONC direction: keep ghost.env for the initial release, introduce the manager with S4 backup/restore, and retain config helpers until their host callers have a verified offline replacement.

Validation:

• Existing helper/Docker suite: 235 passed.
• Bash 3.2 with an unavailable daemon, including new HTTP and image-resolution regressions: 111 passed.
• Configuration matrix on Compose 2.24.0 and 5.1.2: 198 passed.
• Readiness against the actual optional-service dependency graph, using disposable commands: all 6 minimum/current cases passed (completed jobs, failed migration, unhealthy Ghost).
• Real installer end-to-end suite: 21 passed, including concurrent local sites, production HTTPS, existing proxy protection and restricted host tools.
• ShellCheck 0.10.0 and 0.11.0 passed; no whitespace errors.

The first readiness run exceeded the test-runner timeout during fixture shutdown. Fixtures now use a one-second shutdown grace period, and the compatibility rerun passed. No manager implementation or changes to existing stack branches are included.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 5d776cce-f109-44e5-a7c1-361e2712e202

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

_{Comment @coderabbitai help to get the list of available commands.}