Install & customize Spec-Kit for spec-driven development in core

[nollymar]

Description

Install and customize GitHub Spec-Kit (v0.12.4, Claude Code skills) in dotCMS/core to support spec-driven development, tailored to dotCMS's specific needs:

1. Legacy-aware — the codebase mixes modern com.dotcms.* and legacy com.dotmarketing.*; specs and plans must account for that rather than assuming greenfield.
2. ADRs feed the plan phase — ADRs live in the private repo dotCMS/platform-adrs. /speckit-plan must always consult relevant ADRs as binding input.
3. Spec-Kit must never create ADRs — it may only propose them; ADRs are authored in platform-adrs via its own new-adr.sh process.
4. Two spec flows — separate templates/commands for new features vs. issue/bug resolution.

Implemented in PR #36416.

Acceptance Criteria

• Spec-Kit installed (.specify/) and /speckit-* skills available for Claude Code, additive (no existing files clobbered)
• Constitution encodes legacy-aware development + dotCMS Critical Rules and is loaded by every skill
• /speckit-plan consults dotCMS/platform-adrs automatically (read-only via gh), surfacing relevant ADRs as binding input, with an ADR Alignment gate in the plan output
• Spec-Kit never creates/edits/commits ADRs anywhere; it only proposes them (guardrail enforced in constitution + skills + plan template)
• Two spec flows exist: /speckit-specify (new feature) and /speckit-specify-fix (issue/bug resolution), both funneling into /speckit-plan
• Customizations are upgrade-safe (overrides + net-new files) and documented in .specify/CUSTOMIZATIONS.md

Priority

Medium

Additional Context

• PR: chore(speckit): install & customize Spec-Kit for dotCMS (legacy-aware, ADR-gated) #36416
• Docs: .specify/CUSTOMIZATIONS.md (rationale + upgrade re-apply notes)
• ADR lookup is read-only via the authenticated gh CLI against dotCMS/platform-adrs — no clone/submodule.
• The native Spec-Kit bug extension was intentionally not used because its assess→fix→test flow bypasses /speckit-plan (and thus the ADR gate).

[nollymar]

Update — TDD gate added (part of this task, in PR #36416).

TDD is now a non-negotiable gate in the Spec-Kit workflow. No implementation code is written before:

1. Tests are written (unit / Postman / integration / Karate / e2e as applicable)
2. Tests are validated and approved by the developer — and if a test type genuinely can't be implemented, the developer must explicitly say which and why ("no tests" is never a default)
3. Tests are confirmed to FAIL (Red)

Enforced at three layers (all upgrade-safe, no shipped Spec-Kit files edited):

• Constitution Principle V → Test-First / TDD (NON-NEGOTIABLE) (v1.1.0), loaded by every skill.
• tasks-template override → tests mandatory; every user story ordered Tests → [GATE] dev approval → [GATE] Red → Implementation.
• plan-template override → Test Strategy section + Principle V in the Constitution Check gate.

[github-actions]

PRs linked to this issue

• chore(speckit): install & customize Spec-Kit for dotCMS (legacy-aware, ADR-gated) by @nollymar