chore: add kiro spec-driven tooling and steering docs

Add the Kiro-style agentic SDLC tooling used to drive this project: the
.opencode/skills/kiro-* skill set (discovery, spec init/requirements/design/
tasks, validation, implementation, review, steering), the .kiro/settings
templates, and AGENTS.md describing the workflow. Update the spec docs
(assessment/design/requirements/tasks) to current state.

Scope tests/test_opencode_skills.py to the project's own openultrasast-*
skills so the third-party kiro-* tooling (which uses a different frontmatter
convention) no longer breaks the frontmatter check.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

.kiro/settings/templates/steering-custom/database.md

@@ -0,0 +1,46 @@
+# Database Standards
+
+[Purpose: guide schema design, queries, migrations, and integrity]
+
+## Philosophy
+- Model the domain first; optimize after correctness
+- Prefer explicit constraints; let database enforce invariants
+- Query only what you need; measure before optimizing
+
+## Naming & Types
+- Tables: `snake_case`, plural (`users`, `order_items`)
+- Columns: `snake_case` (`created_at`, `user_id`)
+- FKs: `{table}_id` referencing `{table}.id`
+- Types: timezone-aware timestamps; strong IDs; precise money types
+
+## Relationships
+- 1:N: FK in child
+- N:N: join table with compound key
+- 1:1: FK + UNIQUE
+
+## Migrations
+- Immutable migrations; always add rollback
+- Small, focused steps; test on non-prod first
+- Naming: `{seq}_{action}_{object}` (e.g., `002_add_email_index`)
+
+## Query Patterns
+- ORM for simple CRUD and safety; raw SQL for complex/perf-critical
+- Avoid N+1 (eager load/batching); paginate large sets
+- Index FKs and frequently filtered/sorted columns
+
+## Connection & Transactions
+- Use pooling (size/timeouts based on workload)
+- One connection per unit of work; close/return promptly
+- Wrap multi-step changes in transactions
+
+## Data Integrity
+- Use NOT NULL/UNIQUE/CHECK/FK constraints
+- Validate at DB when appropriate (defense in depth)
+- Prefer generated columns for consistent derivations
+
+## Backup & Recovery
+- Regular backups with retention; test restores
+- Document RPO/RTO targets; monitor backup jobs
+
+---
+_Focus on patterns and decisions. No environment-specific settings._