Replace releases with Deployments (automatic, per environment) and project Milestones (deliverables measured by what's live)

Part of PAR-357. Rewritten 2026-10-18 after Rían asked to move away from big-bang "omega" releases. Design: PR #34, stories "Deployments" and "Project + milestones".

Why

Today a "release" is a frozen snapshot of one develop→main PR (V15__releases.sql: release + release_issue, frozen on merge). That models big releases cut by a person. The real flow is many small PRs merging continuously. Each one previews on development, and a merge to main deploys to production through Argo/Image Updater, often carrying several PRs at once.

New model

Deployment: an automatic record of code reaching an environment.

• environment (development / production; configurable per project)
• sha, deployed_at, source (Argo, GitHub Actions, manual), state (live / superseded / rolled back / preview)
• the PRs it contains, resolved by merge SHA range since the previous deploy to that environment, and through them the issues
• Dev deploys correspond to PR previews ([DEPLOY] commits); production deploys correspond to merges to main.

Milestone: a deliverable inside a project, e.g. "Sales tax v2".

• name, goal (one line), health (on track / at risk / paused / shipped), with issues assigned to it
• Progress is measured by delivery, not closure: count issues at each stage (tracked → PR open → merged → on dev → live). An issue counts as "live" once a production deployment contains a PR that references it.
• No target dates (decision: no due dates in the UI).

Do

Backend

• New tables deployment, deployment_pr and milestone (+ issue.milestone_id).
• Ingest GitHub deployment / deployment_status webhooks, and/or an Argo CD notification webhook. Fall back to treating "push to main" as a production deploy when there's no deploy signal.
• Link PRs to deployments by SHA range. Derive each issue's delivery stage.
• Migrate release rows to milestones (shipped) plus historical deployments, then drop the release tables and ReleaseMcpTools. Add MCP tools for deployments and milestones.

UI

• Deployments page: a current-state card per environment ("live for 2h · 2 PRs · 3 issues"; "#84 and #87 on dev, not yet merged"), then a day-grouped feed of deploys with PRs, issue refs, the milestone tag and state.
• Project overview: a milestones list with the five-step flow counts; expand to see each issue's delivery track and the deploy it shipped in.
• Issue detail: the Development panel shows the delivery track and "Live since deploy e77d310".
• Remove the Releases nav item and pages.

Acceptance

• Merging a PR to main that references PAR-123 shows PAR-123 as Live once the production deployment lands, with no manual step.
• A rolled-back deploy moves its issues back to "merged".