feat(habit): add tenant-safe PostgreSQL repository

[seonghobae]

Summary

Implements #39 as the next reviewable slice of #36.

• adds a parameterized PostgreSQL implementation of the asynchronous Habit repository contract
• encodes normalized ISO weekdays into the persisted seven-bit mask and validates recurrence invariants on reads
• validates UUIDv4 identifiers, IANA timezones, local dates, RFC 3339 timestamps, titles, tenant ownership, expected lookup identifiers, and result cardinality
• scopes every lookup by workspace_id and aligns deterministic reads with the migration indexes
• inserts completion history append-only and recovers exact retries only after the named idempotency constraint reports a unique violation
• rejects an idempotency-key replay whose scheduled date or completion timestamp differs from the original event
• maps unrelated driver and transport failures to a credential-free HabitPersistenceError without misclassifying them as retries
• adds unit evidence for SQL binding, recurrence encoding/decoding, malformed persistence rows, tenant crossover, missing/duplicate lookups, new completions, exact retries, conflicting retries, safe database failures, and completion ordering
• executes the Habit migration against CI PostgreSQL and proves restart durability, tenant isolation, concurrent duplicate serialization, conflicting replay rejection, and database-enforced UPDATE/DELETE/TRUNCATE protection
• documents the exact slice, deferred runtime work, and validation gates

Deferred

Validated production pool configuration, NestJS lifecycle wiring, HTTP endpoints, RFC 9457 persistence errors, and higher-level habit workflows remain separate reviewable slices.

Validation gate

Merge only when CI, AppGuardrail, Semgrep, Security Scan, Commercial Readiness, CodeRabbit, and all human/security review requirements pass on the exact head with no unresolved actionable findings.

Closes #39

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📥 Commits

Reviewing files that changed from the base of the PR and between f3ea399 and beb0000.

📒 Files selected for processing (9)

• .github/workflows/ci.yml
• apps/habit-service/migrations/README.md
• apps/habit-service/package.json
• apps/habit-service/src/postgres-habit-repository.integration.test.ts
• apps/habit-service/src/postgres-habit-repository.test.ts
• apps/habit-service/src/postgres-habit-repository.ts
• docs/superpowers/plans/2026-08-04-habit-postgres-repository-slice.md
• package.json
• turbo.json

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