Add Zod dependency and update API interfaces

- Added Zod as a dependency in package.json.
- Updated pnpm-lock.yaml to include Zod.
- Refactored API interfaces: exported new modules for perk, survivor, mission, and encounter.
- Removed obsolete api-interfaces.ts file.
- Enhanced tests for new schemas in api-interfaces.spec.ts, covering various validation scenarios.

docs/adr/README.md

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+# Architecture Decision Records
+
+This directory contains ADRs for Fog Expedition — durable records of architectural choices, why they were made, and what trade-offs they imply.
+
+## Format
+
+We use [MADR](https://adr.github.io/madr/) (Markdown ADR) format. Each record has:
+
+- **Status** — proposed, accepted, deprecated, or superseded
+- **Context and problem statement** — what situation forced a decision
+- **Decision drivers** — the factors that mattered
+- **Considered options** — what we looked at
+- **Decision outcome** — what we chose and why
+- **Consequences** — what this means going forward, good and bad
+
+## Index
+
+| # | Title | Status |
+|---|-------|--------|
+| [0001](./0001-twitch-extension-type.md) | Twitch Video Overlay over Panel extension | Accepted |
+| [0002](./0002-nx-monorepo-with-strict-boundaries.md) | Nx monorepo with enforced module boundaries | Accepted |
+| [0003](./0003-mixed-test-runners.md) | Vitest in libs and overlay, Jest in API | Accepted |
+| [0004](./0004-stateless-seeded-encounter-resolver.md) | Encounter resolver as pure library with seeded PRNG | Accepted |
+| [0005](./0005-per-mission-jittered-tick-scheduling.md) | Per-mission jittered tick scheduling | Accepted |
+| [0006](./0006-postgres-plus-redis-data-split.md) | PostgreSQL for durable state, Redis for ephemeral | Accepted |
+| [0007](./0007-devcontainer-with-host-services.md) | Devcontainer with docker-outside-of-docker, services on host | Accepted |
+
+## When to write a new ADR
+
+Write one when:
+
+- The decision has plausible alternatives that reasonable people might pick differently
+- The reasoning will matter six months from now
+- The decision shapes how the codebase evolves
+
+Don't write one for:
+
+- Style or convention (those go in `CLAUDE.md`)
+- Decisions with one obvious answer (no real choice was made)
+- Implementation details that change frequently (those go in code comments)
+
+## Superseding
+
+If a future decision overrides one here, mark the old one's status as `Superseded by ADR-NNNN` and link forward. Don't delete superseded ADRs — the history is the value.