v1.2.1 — Portability cut

The portability cut: everything a stranger needs to install, configure, and run the plugin without access to the original development network.

• Provider config genericized — templates/providers.yaml.template, opencode.jsonc, schema descriptions, and the /sdd-init wizard now use generic local / anthropic-hosted lanes on localhost endpoints instead of the original homelab endpoints. Same schema, same semantics; provider names remain free-form.
• STE-100 writing standard merged — rules/ste100-writing.md (an original ASD-STE100 adaptation for software specs) wired through sdd-spec, sdd-plan, sdd-adr, the PRD self-audit, and the sdd-skeptic checklist. 16 contract tests. Spec: context/specs/spec-ste100-docs.md.
• Reviewer role depersonalized — the UX-validation reviewer is "the operator" throughout agents, skills, and schemas (formerly a named person); example personas in templates are fictional.
• Tree focused on the plugin — the Electron Build Lab app and Ink TUI archive extracted (recoverable at commit 44e8fe6; Build Lab graduates to its own repo), Build-Lab-era working artifacts pruned, completed PRDs archived, runtime state (progress.txt, .sdd/handoff.json) removed and gitignored.
• CI on GitHub Actions — new tests.yml (vitest suite, server build, OpenCode smoke, shell docs-contracts, provider-template validation); install-archive parity workflow ported from Forgejo CI unchanged; ux-test-lint path fix.
• Version + surface truth — server manifest aligned (was 1.1.1 / MCP constructor 0.3.0); MCP surface corrected to 19 registered tools (ux-runs registers list+read from one file); docs-contract test now counts actual server.tool() registrations.
• Dogfood suite guards — Constellation-sibling assertions skip cleanly when the sibling checkout is absent: fresh clones run 571 passed / 12 skipped.
• Docs rebuilt for a public audience — README restructured (dogfood showcase, honest portability boundary, GitHub install), changelog extracted to this file, CONTRIBUTING added.